Molecular Films, The Cyclotron, and The New Biology: Essays [Reprint 2022 ed.] 9781978811690

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Rutgers University

- PUBLICATIONS O F T H E O N E H U N D R E D

SEVENTY-FIFTH ANNIVERSARY

CELEBRATION

Number Four

Molecular Films, The Cyclotron, and The N e w Biology

MOLECULAR FILMS

The (t Cyclotron ¿r 9 THE NEW BIOLOGY Sssays by HUGH

STOTT TAYLOR

ERNEST O. L A W R E N C E IRVING LANGMUIR

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RUTGERS UNIVERSITY PRESS 1942

C O P Y R I G H T 1 9 4 a B Y T H E T R U S T E E S OF R U T G E R S C O L L E G E IN N E W J E R S E Y

Printed in the United States of America

Contents Fundamental Science from Phlogiston to Cyclotron By

H U G H STOTT T A Y L O R

Molecular Films in Chemistry and Biology By

63

ERNEST O. LAWRENCE

Commentaries By

27

IRVING LANGMUIR

Nuclear Physics and Biology By

3

LESLIE A . CHAMBERS and J . R .

87 DUNNING

Molecular Films, The Cyclotron, and The New Biology

Fundamental Science from Phlogiston to Cyclotron H U G H STOTT TAYLOR H E life span of Rutgers University coincides almost exactly with that of modern science. During these one hundred and seventy-five years science has traveled the thronged highway from phlogiston to cyclotron. It has emerged from the laboratories of isolated, individualistic experimenters into the highly organized, cooperative undertakings of the universities, the research foundations and the industrial enterprises of today. Paralleling the phenomenal growth in scope is the determinative influence that it has come to exercise on all phases of modern life. The rapidity of that growth has brought with it all the corresponding problems of assimilation into the life of the community. The world today is suffering in many respects from its inability to solve such problems satisfactorily and science, it is suggested, bears a major portion of the blame. As Professor A. A. Bowman points out in the introductory sentences of his posthumous volume "The Sacramental Universe": "The age in which we live is notable for two things: man's progressive triumph over nature in the sphere of theoretical and applied science, and his tragic inability to order his own life. Every year adds appre-

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ciably to our knowledge of the physical world: every year brings home to us the baffling inscrutability of human nature as revealed in our disordered civilization." Of necessity, in the ideal human society to which we must look forward, the scientific aspects of life must be assigned their due proportions - they must not be "cribbed, cabined and confined," but neither must they be permitted to crowd out from our lives the humanistic, the social and the spiritual values that are equally necessary and indispensable. In the formulation of that ideal society it will be important to know the "stages on the road'' whereby science has emerged to so dominant a position in the body politic, to learn something of the factors that have led to the rapid advances that have been made, to trace some of the interactions between one science and another, between the physical and natural sciences, which have undoubtedly contributed to that advance and growth. An occasion, such as the present, with its opportunities for survey and reflection, for retrospect and prospect, prompts the effort to evaluate some of the fundamental scientific aspects of the problem, to examine the broadening bases of the whole structure, the increasing availability of new tools of investigation and the consequent increasing tempo of scientific advance. The study will center largely around advances in chemistry, physics and physiology, their interactions one with another. These, it is hoped, are typical of other sciences and may exemplify the whole problem in such a way as to indicate what the future may hold, what we may expect and hope for by the time this University C O

celebrates its second centennial of service to education, to learning and to knowledge. Eighteenth century science had begun in the brilliant sun of Newton's discoveries. One might have expected that rapid developments would follow. There was, however, a time lag; assimilation came slowly and it was not before the first twenty-five years of Rutgers' history had arrived that the ripening of ideas brought forth its abundant fruit. From the earliest times chemistry on the one hand and physiology on the other had been intimately associated with and dependent upon the concepts of the physical. The early decades of the eighteenth century were characterized by an increasing degree of specialization and of concentration on particular fields of study. The chemical revolution which marked the closing of the century was one evidence of this specialization. Black ushered in the era with his decisive experiments in 1754 on carbon dioxide. Scheele, Cavendish and Priestley contributed their quotas of new gases which ultimately destroyed the concept of phlogiston that "notorious doctrine of an element of negative weight." Chlorine, hydrogen and oxygen were the important trio, the latter providing the master-scientist of the French Revolutionary era, Lavoisier, with the bases for a theory of combustion as a result of which phlogiston was finally if slowly abandoned. These were the first fruits of an experimental science in which were combined manipulative skill, observational ability and, above all, the quantitative method. Its immediate consequence, the law of conservation of mass (1774), formed the basis of much of the quantitative analytical C53

work of the early nineteenth century. I t fitted admirably into the framework of chemical principles established by Dalton's Atomic Theory (1808) which marks memorably the second period of our review. The atomic theory in its turn led to the correct correlation of the concept of atoms and molecules with the physical properties of gases as embodied in the laws of Boyle and Gay-Lussac as formulated by the famous hypothesis of Avogadro ( 1 8 1 1 ) . Two events, concerned with scientists whose work we have just discussed, serve graphically to define the general suspicion, if not hostility, toward science and scientists at this time. We need only recall the violence wreaked on Priestley's laboratories in Birmingham because the discoverer of oxygen and a famous dissenter was known to be sympathetic to the revolutionary ideas of France, so that, like so many scientists in recent history, he was forced to take the westward way to a haven in America. On the other hand, the Terror was claiming its victims in Paris with the well-remembered dictum of Lavoisier's judge "The Republic has no need for scientists; let justice take its course." The chemical revolution had a definite impact both on physiology and physics. The recognition of carbon dioxide and water as the products of animal respiration by Lavoisier and Laplace constituted a milestone of progress in physiology due to chemistry comparable with Harvey's contribution on the physical principles operative in the circulation of the blood, early in the 17th century. The interdependence of the plants and animals, recognized by Ingenhousz in 1779, stems from

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the same discoveries. Lavoisier recognized in his "Traité Elémentaire de la Chimie" the necessity of a material theory of heat and christened it "caloric"; scientists of the quantum generation may recall with interest that both heat and light were included in his table of chemical elements. It was when Rutgers was about twenty years old that from the physiological observations of muscle-nerve preparations of frogs' legs by Galvani (1786) and the association of these by Volta with a current produced by connection of dissimilar metals that there resulted the development of the voltaic pile (1799) with all the many consequences in physics and electro-chemistry. The decomposition of water with the electric current by Nicholson and Carlisle (1800) and the important researches of Davy, first with salt solutions, and later with fused salts leading to the isolation of the alkali metals, sodium and potassium (1807), were immediate and obvious consequences of these discoveries in the realm of chemistry. The implications for physics came later. D a v y , in his work on chlorine and hydrogen chloride, not only established the elementary nature of chlorine but indicated that oxygen was not so fundamental in the make-up of acids as Lavoisier had envisaged. Berzelius (1779-1848) built the concepts of electricity into chemical thought with his dualistic theory and supplemented his theoretical concepts with a prodigious output in preparative inorganic chemistry and the quantitative analysis of the preparations. The interactions of physics and physiology are well illustrated also in this era by Young's studies of the eye, leading to his

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consideration of the colored pigments and colored light, the sensitivity of units in the retina to three primary colors. Dalton's researches on color blindness belong to the same period. The twenty-five years which succeeded the Battle of Waterloo found science advancing in all its branches with increasing tempo and with marked interactions. Physics went forward with the elucidation of the interaction between currents and magnets, by Oersted in Copenhagen (1820) and Ampère in France. Ohm's work (1826-27) o n conductors gave us the now familiar relation between current, resistance and potential. Faraday in England and Joseph Henry in this country, early in the 1830's, recognized the phenomenon of induction and thus laid the bases for the electrical age. Faraday's Laws of Electrolysis connecting quantity of electricity with amount of electrochemical action not only interlocked more closely the sciences of chemistry and electricity but were the first indications of the unitary nature of electricity, definitely formulated by Stoney (1874) a n d Helmholtz (1881) and culminating in the "natural unit of electricity," the electron (1891). The interconvertibility of energy, of motion into heat energy, of electrical energy into heat energy, the discovery of thermo-electricity in 1820, the production of heat and electrical energy by chemical interactions, the brilliant researches of Carnot on the availability of energy, were preparing the ground for the enunciation, in the next of our epochs, of the law of conservation of energy. Wòhler's synthesis of urea from "inorganic" sources 8

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(1828) and the recognition of its identity with "urea" from urine provided the first organic synthesis and initiated the science of organic chemistry. Liebig beginning in the thirties developed the science of physiological chemistry by application of specialized organic chemical techniques. The nitrogenous proteins in plants had been recognized by Magendie in 1819 as essential in animal nutrition and suggested to Liebig the problem of practical assistance to agriculture in the form of nitrogenous fertilizers. One hundred years ago the time was ripe for important theoretical developments in science. In 1842 the definite statement of the equivalence of heat and work came from Mayer. Carnot had foreshadowed this in his considerations concerning the availability of energy deduced by means of his famous engine working in a cycle. I t was Helmholtz, however, who pointed out, in 1847, that the equivalence of heat and mechanical energy is a special case of a general law of energy conservation. I t is significant that these physical principles were enunciated by Mayer, a doctor, and Helmholtz, a surgeon, and that the consequences of this generalization had already been applied to chemical reactions by Hess, in 1840, prior to the formal statement of the general law, in the Law of Constant Heat Summation upon which is based the science of thermochemistry. Joule and Thomson (Lord Kelvin) gave the conservation law its experimental verification, while Clausius (1850) and Thomson (1851) gave statements of the Second Law of Thermodynamics which Clausius restated later (1854) in terms of his famous "entropy." To quote the aphor-

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ism of Clausius, science became aware that " T h e energy of the universe is constant; the entropy of the universe is ever tending towards a maximum." Gibbs and Helmholtz developed the concept of free energy and established the inter-relations of free energy, total energy and entropy that now, for nearly one hundred years, have been the tools of engineer, physicist and chemist. I t is to this same period, also, that the famous electromagnetic field theory of Maxwell belongs. Generations of physicists were to be trained in the details of the Maxwellian equations with the aid of the mathematics of Laplace and Lagrange. Not until the dawn of the present century were models to return to the phenomena of electricity and light. Late in the nineties and early in the present century would there be a return to electrons and to photons. The practical applications of Maxwell's theory came later. The principle of the telephone came with Bell in 1875. Hertz verified the electromagnetic waves first in 1887 and their practical applications in radio-telegraphy were postponed until this century. I t is not possible, within the scope of our present inquiry, to follow through, in detail, the progress which the biological sciences were making in morphology and embryology, in cell structure and development. We note, however, that it is in this same period of intense development of theoretical physics that the doctrine of evolution took definite form. Darwin's "Origin of Species" was published in 1859. The Mendelian researches on heredity came late in the same era (18571866). Pasteur, after his earlier researches on tartrates

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that resulted ultimately (1874), through van't Hoff and Le Bel, in the chemistry of atoms in three-dimensional space, established decisively in 1861 the significance of micro-organisms and the absence of spontaneous generation. These ideas he applied to the silkworm industry of France (1862-65). Lister's application of Pasteur's observations to surgery and his concept of sterilization date from 1865. Chemical theory was advancing also. Frankland's idea of valency (1852) was given definite application to organic chemistry by Kekulé's insistence on the tetravalent carbon atom. Cannizaro, at the famous conference in Karlsruhe in i860, restated with conviction the hypothesis of Avogadro as the principle through which order and agreement might be brought to chemical symbolism. Newlands in 1864 pointed out the recurrence of elements in octaves and though his fellow scientists in England laughed him to scorn, his views were contained in the larger synthesis of Mendeléeff's Periodic Law (1869-71). It is significant that just seventy additional years had passed before the final gaps in the list of 92 elements were closed a year or so ago; the law remains as a fundamental classification factor in chemical science. Philosophically, it foreshadowed, although this was by no means fully realized, a unitary theory of matter. The similarity and periodicity of properties both chemical and physical (Lothar Meyer), is the strongest possible evidence that like elements must possess a similarity of atomic architecture not envisaged by a Daltonian theory of indivisible atoms. Further consequences of theoretical development in

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this era may be noted in the recognition of the two great classes of organic compounds, the aliphatic and the aromatic groups. Aniline was recognized in the latter group with benzene by Hofmann in 1843 and his pupil, Perkin, discovered the first aniline dye, mauve, in 1865. Kekule reconciled the existence of benzene with his four-valent carbon atom by means of his famous hexagon of carbon atoms in the same year. Tools of practical importance in science from the same period include the Bunsen burner and the development of the spectroscope and spectroscopic analysis by Kirchhoff, Bunsen and Roscoe in the years around 1855. This last tool is a good example of how progress in one field of science affects others; astronomy, physics and biology all turned this tool to significant use. The record of the first century of the era under review has thus been outlined. We approach with some trepidation the sketch of the giant development which the tree of science underwent in the remaining seventy-five years. It is obvious that our outline must of necessity become more and more eclectic, that we must suggest, rather than detail, the main lines of growth. In the years from 1866 to 1891 progress in physics proceeded at a more leisurely pace. Some imagined that there was little still to be discovered and that increased precision and refinement of measurement were the lot of the physicist. It was, however, the age in which were developed by Maxwell and Boltzmann that principle of equipartition of energy among the degrees of freedom of an assembly of molecules which was basic to the classical phase of statistical mechanics and the thermo12

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dynamics of radiation, both of which were to remain until the concept of quanta developed by Planck in the succeeding 215-year period required their fundamental modification. The conception of the electron, atom of electricity, was developed, as earlier mentioned, by Stoney and Helmholtz. The spectral series of hydrogen lines discovered by Balmer (1885) was the first of a sequence of observed regularities in spectra which culminated finally in the Bohr theory of orbits. Hittorf's discovery of phosphorescence produced from cathode rays (1869), Crookes' deflection of these by a magnetic field (1879) were but glimpses of the golden decades immediately ahead. Chemistry, on the other hand, experienced a blossoming-time. Guldberg and Waage had just defined the Law of Mass Action (1864-67), placing chemical equilibrium upon a firm theoretical basis. Gibbs supplied the general equations governing equilibria in systems of many components (1875-78) which became, in the Phase Rule (1877), the instrument for defining conditions of stable existence of many and varied systems. Le Chatelier and Braun (1888) laid down the principle of mobile equilibrium which determined the shift in equilibrium produced by changes of temperature and pressure; thermodynamic equations, such as that of Gibbs-Helmholtz, gave the quantitative expression to such changes. I t was, however, as a result of electrochemical investigations, the transport numbers of Hittorf (1859), the refined conductance measurements of electrolytic solutions by Kohlrausch (1879) combined with the fundamental studies of Raoult on the molecular C »s 3

weights of dissolved salts and Traube's researches on osmotic pressure membranes in porous pots (1867) with Pfeffer's researches (1877) on osmotic pressure measurements which provided the bases upon which a new science of physical chemistry could be constructed through the genius of van't Hoff and Arrhenius and the organizing skill of Ostwald. Wilhelmy's pioneer investigations on reaction kinetics were generalized by van't Hoff, and his data on the velocity of inversion of cane sugar were re-interpreted in terms of hydrogen- and hydroxyl-ion catalysis. The ground-work was prepared for the quantitative study of catalysis not only in homogeneous systems but also for those many processes of heterogeneous catalysis, collected by Berzelius, which included the oxidations of gases studied by Dobereiner, D a v y , Turner, Henry and Phillips. Earlier in the century, these had received so masterly a study by Faraday in his inquiry into "the power of metals and other solids to induce the combination of gaseous bodies." Equipped thus with the fundamentals of equilibrium, properties of solutions and the laws governing the velocity of reaction, chemical industry could go forward with sure step to its developments in the pre-war era from 1890 to 1914. In the field of organic chemistry the development of synthetic skills produced large numbers of new compounds many of great significance for future studies in the developing science of biochemistry. Lactic acid was shown to be the oxidation product of carbohydrate (1867-71). The attack on the constitution of the sugars began in earnest in the 1880's and has provided its own peculiar problems even down to recent days. Fischer's

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successes in this field led to his more ambitious programs in the subsequent years (1894-1919) on the uric acid group and finally in the protein field. Only with the great resources of experimental techniques now available are the problems of giant molecules such as the starches, proteins, rubber and the synthetic polymers yielding their well-kept secrets. All of these developments paved the way for a corresponding intensive development on the biological side which rapidly incorporated the quantitative aspects of physical chemistry and the increased knowledge of constitution that came from the synthetic organic work. There remain now for consideration two main divisions of scientific progress, that between 1891 and the middle of the first World War and that which has been described as "Interbella," which brings us down to our own days. These are the epochs which have knit science so closely into the fabric of everyday life, where the consequences of scientific discovery have been rapidly translated into the victories both of peace and, unhappily, of war. Each branch of physical and natural science went swiftly forward. Each borrowed from the others its newest tools, its developing techniques, to fashion with them new advances in the scientific age. Where to begin, what to omit are the real problems which face the recorder of these paths of progress. Experimental physics entered its golden age in the "golden nineties." Rontgen discovered X-rays in 1895 and presently surgeons were examining the skeletal structure of man. J . J . Thomson (1897) measured the conductance of gases at low pressures and gave us the C >5 3

fundamental properties of the electronic constituents of all matter, with a mass nearly one two-thousandth of the lightest atom, hydrogen. Becquerel, 1896, found penetrating radiations from substances containing uranium and thorium, which led to the isolation by the Curies of radium, polonium and other elements. Rutherford defined the nature of the radiations emitted and with Soddy propounded the general concept of radioactive breakdown of atoms to smaller atoms with emission of radiations, one of which proved to be helium. Radium sources passed immediately into the surgeon's hands as a supplement to X-ray therapy. The X-rays and 7-rays were recognized as light of extremely short wave length and Laue (1912) utilized the crystalline state to determine the wave lengths while the Braggs (1913) put X-rays to the task of determining the architecture of crystals. Moseley (1913) showed that the characteristic X-ray frequencies of the elements yielded a surer test of the order number of the chemical elements than the periodic classification of Mendeleeff had provided. Soddy, following the chemical transformations accompanying the radioactive changes, arrived at the concept of "isotopes." J . J . Thomson and Aston (1912), returning to an examination of the "positive rays" accompanying conductance in gases, found evidence that neon might exist as non-radioactive isotopes with masses 10 and 11. Barkla (1911) examined the scattering of X-rays by atoms and Rutherford ( 1 9 1 1 - 1 3 ) that of aparticles by atoms and the concept of the nuclear atom took form. Theoretical physics took a revolutionary turn at the

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dawn of the century. Planck recognized that the accurate data on the distribution of light intensity with wave length from hot bodies could not be interpreted on the older theory of light energy as a continuum. The quantum theory was born; atomistic light joined the ranks of atomistic electricity and matter, although already in this latter case the results of radioactive study were demanding a revision of the concept of indivisibility. Lenard's data on the photoelectric effect, Einstein's extension of the Planck concept to visible light and to photo-absorption by molecules were but the preludes to the Bohr theory of the atom which provided a basis for the scientific analysis of atomic and subsequently molecular spectra. The relativity theory emerged with its generalized mass-energy relationship which now is used daily by elementary students to interpret transmutational changes; which gave us also our clue to the energy sources in the sun. Chemistry in the same interval was broadening the physico-chemical bases of the science. Ramsay's discovery of the rare gases and the new problems raised by radioactive change provided new avenues of investigation. The interval preceding 1916, however, is startlingly characterized in chemical science by the intensive development of applied chemistry utilizing the theoretical principles of equilibrium and reaction velocity, the conclusions of the newer physico-chemical science especially as to the role of catalysts in chemical reaction and the rapidly increasing synthetic skill of the organic chemistry. This was the period in which a prodigious development of chemical industry occurred in Europe, prinC

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cipally in Germany, characterized by the contact sulfuric acid process, the dependent dye-stuff industry, including especially synthetic indigo, the hardening of liquid fats to produce soap materials and edible fats and finally, on the eve of the first World War, the synthetic ammonia development which solved a world nitrogen problem and introduced the techniques of high pressure to chemical industry. It was an age in which the demands of industry were exhausting the funds of theoretical science. New wells of fundamental scientific knowledge would be needed for the new generations of applied science. It is now a matter of history that up to 1914 the revolution in applied chemistry had scarcely touched America; the chemical industry was a mere infant as the war clouds broke; but America, through the researches of Irving Langmuir, first on the reactions of gases at the surfaces of a tungsten filament lamp and next on the orientation of molecules in insoluble films at the surface of water, was already providing the fundamental bases upon which, in the next generation, not only chemical science but biochemical science could be still further enlarged. Langmuir's researches taught the chemist the short ranges of chemical forces and the stability of unimolecular layers. Chemists began to think of molecules in terms of their length and breadth and cross-sectional areas, the conclusions reached from oriented films and X-ray pictures conforming excellently with the inductive reasoning of the organic chemist. In the biological field the idea of internal secretions, which was emphasized in the 1850's by Claude Bernard, took on new activity in the same pre-war era. Pavlov

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was working on nervous reflexes as the stimulant of digestive agents. Adrenaline from the adrenal glands was isolated, identified and synthesized. The hormones or chemical messengers date from the work of Bayliss and Starling on "secretin" in 1902. As the pre-war era closed Kendall (1914) had isolated an iodine compound from thyroid gland which Harrington was to characterize and synthesize in 1927. An internal secretion from the "Islets of Langerhans" in the pancreas was known in 1893, named "insulin" by Schafer in 1913 and which Banting and Best isolated (1921) and turned to use in the treatment of diabetes. The concept of deficiency diseases, which led to the close integration of the organic chemist and the physiologist in this, the vitamin era, became evident from the work of Eijkman (1897) on beri-beri from polished rice, from the work of Hopkins (1906) on synthetic diets and of McCollum and Davis in America from 1913 onwards. Between 1913 and 1916, fat-soluble A, the growth-producing vitamin, was separated from the water-soluble fraction which afterwards became the famous vitamin B complex. Vitamin C, the anti-scurvy agent in citrus-fruits, was identified in 1913. Gradually vitamin D, the anti-rachitic, cod-liver-oil vitamin, gained an identity separate from vitamin A. And, now, the final breathless twenty-five years. Rutherford's artificial disintegration with swift a-particles set the stage, immediately in the post-war period, for the old dream of the alchemist, transmutation of the elements, in its new title, nuclear physics. The age ahead was the era of exploration of the architecture C >9 3

of the nucleus, the age of "atom smashing." The man in the street, even, became familiar not only with electrons and protons but also with neutrons. The study of isotopes, proceeding concurrently, gave us, at the psychological moment, heavy hydrogen, the deuteron combining the efficiencies of proton and neutron. The techniques developed for deep X-ray therapy were applied to the production of high speed protons and deuterons, with energies so high that the lowly kilo-volt gave place to a new unit, the million-electron-volt (m.e.v.); these high speed particles were hurled by Cockcroft and Walton at the lithium atom to give the earliest artificial disintegrations with man-powered atomic bullets. Then, from the Golden West came the story of the new genius, Lawrence, and the new machine, the cyclotron, which by its new principle could give ever-greater momenta to these atomic bullets. Lawrence himself built a sequence of cyclotrons of ever-increasing size from beam energies of 80 kilo-volts to one of 16 million electronvolts, the beam of which extends some 60 inches in air. On the hills above Berkeley there now rises the greatest machine of them all, whose beam, with energies from 100 to 300 million-electron-volts, may be expected to penetrate the colossal distance of 140 feet of air. In that path what phenomena of artificial transmutations of the atoms will occur! From isotope studies, from neutron bombardments and atom-smashing machines, we now possess all the ninety-two elements of the periodic system, in 277 stable isotopic varieties, nine naturally occurring radio-elements and, at a minimum, three hundred and fifty C 20

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artificially produced radio-elements. All these latter have been identified in a feverish pace of research subsequent to the identification of the neutron by Chadwick in 1932 and the first observations on artificially produced radioactive materials by the Curie-Joliots in 1934. Some of the consequences of the cyclotron work in physical and biological science we shall learn today from the pioneer, Lawrence himself. Here we may but mention the interaction between neutron and uranium which yielded nuclear fission, the explosive disruption of the heavy atoms to yield not only the smaller fragments of atoms but, possibly, the long-envisaged goal of "atomic energy." That this last quarter-century has been an age of applied physics, similar to the age of development of applied chemistry that immediately preceded it, is obvious to anyone who takes thought or who contrasts the dominant techniques of World War I with that in progress today. The electron and photo-cell have been harnessed to the development of communications, by radio and telegraph, with and without wires, in Morse code, in voice and by telephoto. It is the contributions of the physicist that are now urgently needed in the "arsenals of democracy" in contrast to the demands on the chemist in 1 9 1 4 - 1 8 . It is true that the development of the aeroplane, tank and motorized equipments have increased the demands made on the fuel technologist. He, however, drawing on the rich reserves of fundamental science based so largely on Langmuir's researches, has competently met those demands in aviation gasoline, improved lubricants, synthetic rubbers, plastics, fibers

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and films, so that the pressure of war demands in this area is small relative to that of twenty-five years ago. If progress on the sub-atomic plane has been spectacular, the developments at the molecular level have been no less noteworthy. Today, in a most striking manner and with an ever-accelerating pace, molecular chemistry and biological science are being integrated. We need only call to mind the synthetic vitamins with structures elucidated, and activities ever better defined, the hormones of sex and of the pituitary and adrenal glands, the new agents of chemo-therapy, sulfanilamide and its successors, the carcinogenec agents so closely related chemically to the sterols, vitamins and pigments, the determination of constitution in the case of haemoglobins and chlorophylls. Techniques have advanced that permit an approach, with confidence, to the problems of high-molecular weight substances, starches, proteins, viruses, enzymes, with weights ranging from 17,000 to many millions, that take us into the domains of the most complex biological systems. The development of the ultra-centrifuge by Svedberg has shown us that these biological systems retain the molecular characteristic, and, with the Tiselius electrophoresis apparatus, demonstrates in many systems the essential homogeneity of the material. Successively, the microscope, the ultra-microscope and, most recently, the electron microscope have increased the resolution of our observations on material objects, so that now it is possible to "see" molecules, if they are as large as the viruses studied by Stanley, and to trace the interaction of one molecule with another. The X-ray analysis of fibers and of

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the simpler globular proteins is now under way and will supplement the analytic and synthetic efforts that characterize this field at the present time. One further aspect of the interaction between sciences must be recorded in the development of biophysics where physical criteria of biological phenomena are receiving most penetrating study, utilizing the newest physical techniques of amplification, through electronics, and recording by photocell, oscillograph, thermo-pile and sound-meter. These delicate instruments permit the study of behavior of single nerve fibers; the physical processes occurring in unit areas of the brain respond to these exploratory devices; and the visual purple of the retina yields its secrets. With all these experimental developments of the era between the wars, theoretical science has not been idle. We have witnessed the consolidation of the wave and particle aspects of radiation in quantum or wave mechanical theory as developed by Schrôdinger, Heisenberg and Dirac and the still more revolutionary proposal of de Broglie that material particles possess a wave nature. Indeed it was this theoretical development that produced the famous tests by Davisson and Germer of the wave nature of the electron and the subsequent application of this to electron diffraction studies of molecules and the electron microscope. The uncertainty principle in physics dates from this period. Theory has ahead a whole new field of exploration of nuclear interaction of which Bohr and his co-workers in Copenhagen and theoretical physicists in this country are the pioneers. As theory and practice interact new horizons will emerge. C 23 3

The record indicates a constantly broadening area of understanding of the phenomena of nature, a geometrically accelerating pace of discovery, a more rapid reaction among the constituent sciences to new knowledge in any one. Increasingly it has attracted the devoted service of its disciples. An impartial humanist and philosopher has recently written of science that "however much science may breed covetousness in man, it itself has remained unsullied by the contaminations of desire. In the modern world," he adds, "science has been the last refuge of sanctity and truth and spirituality." Why then this disease in the modern world and the very prevalent opinion that science has been in large measure responsible for that disease? On the right answer to such an inquiry depends any optimism we may hold for the fate of the future. We are forced to recognize that man cannot live by scientific bread alone. Science is an intellectual technique; it can never be a moral dynamic. Science occupies a sure place in the hierarchy of knowledge, but it can never hold the supreme place. That must be evident when one recalls that the great contributions of science can be used both for good and for evil. Science is the servant of him who would abuse it as also of those who would use it. Had we not realized that, the history of the last dark decade would surely be convincing enough. If we will but recognize these limitations of science, may we not dare, in a time of disaster and terror such as we now suffer, to look optimistically to the coming years ? Cannot our educational efforts gain strength if we but realize that there are orders of "scientia," orders of C 24 3

knowledge, and that we shall fail if we elevate the part to a primacy ? Science which is concerned with knowing in detail and by reason of the proximate or apparent causes can never displace the higher order of knowledge, which we may term wisdom, knowledge "armed for certitude and capable of advancing endlessly in the way of truth." Science will not suffer and life will gain much by frank recognition of these limitations. Science has drawn far away already from the mechanistic, deterministic attitudes that characterized nineteenth century science. The habit still lingers among the less exact of the sciences, and is still more prevalent among the popularizers of science who oftentimes retain into later years their earlier adolescent impressions. To go forward to meet the years of difficulty ahead we shall need the effort of all men of good-will among whom the scientist, by the nature of his calling, must certainly be numbered. The processes of mutual cooperation and assistance among the individual sciences must be multiplied. The isolation of one science from another must become progressively less and less even though the degree of specialization within a science becomes perhaps greater and greater. This calls for an increasing breadth of culture and of education among the scientists, an increasing dedication by the noblest minds to the forward march of knowledge; but it calls also for a fuller appreciation of the social consequences of that knowledge, a franker recognition of the other factors contributory to true knowledge, to wisdom. "The modern world," says Maritain, "by which I mean that world which is coming to

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an end before our eyes, has not been a world of harmony between forms of wisdom, but one of conflict between wisdom and the sciences, and," he adds, "it has seen the victory of science over wisdom." Have not we scientists, so to speak, to surrender that victory? We shall not yield our energy, our courage, our diligence in search of truth. We shall but renounce the primacy to which a sick world has thrust us; and we shall gain by our renunciation. In the free world to which we still dare to look forward, with the soldiers and statesmen, artists, philosophers and priests we shall integrate our scientific skills with the social and spiritual aspects of human life and nature. Let this be, we may pray, an horizon not too distant as Rutgers University approaches its aooth year of service.

Molecular Films in Chemistry and Biology IRVING

LANGMUIR

G O O D account of the history of science has been given by Dr. Taylor, and through it all stands clearly the importance of the interactions between the sciences. Physics has a direct bearing on chemistry and both physics and chemistry determine the growth and progress of biology. So it is, of course, with engineering, astronomy, and all the other sciences that you can name. They are all interrelated. T h e investigations I want to talk about will give an illustration of that. I started out as a chemist interested in mathematics and physics. However, most of the things I have done are essentially in physics, but for some reason or other they are more interesting to chemists and they ought to be most interesting to biologists. I am not a biologist. I cannot possibly apply these things, because I find that I am beyond the depth of my knowledge. I think it is up to the biologist to use the tools that the physicist and the chemist use. I think we have these tools. I am going to talk about the phenomena that take place on surfaces, and I am going to select those things that I think are going to be used in the

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future by the biologist, largely because they are the tools for finding out certain things that he wants to know. Rutgers started 175 years ago. That is a long time; surface chemistry is not much younger than that. The earliest important work was that done by Laplace about 1800. However, I just want to quote from Thomas Young in 1805, because this statement of his, it seems to me, was a great prophecy based on knowledge. He had no ideas about the sizes of atoms in 1805, but in talking about the extent or the range of the forces that were responsible for surface tension phenomena he said: " T h e extent of the cohesive force, that is, range of action, must be limited to about the 25o-millionth part of an inch" - that is about what we measure now in millimicrons - "nor is it probable that any error in the suppositions adopted can possibly have so far invalidated this result as to be many times greater or less." I could not give you a better estimate nowadays of what I think is the most important range of forces as between atoms and molecules. In other words, he struck it just about right, although he was uncertain about it by a factor of four or five one way or another; yet, his estimate was simple and correct. It was based simply on the strength of materials as compared to their surface energies. He knew that, to pull a thing apart and create a new surface, you had to do a certain amount of work, and the work was very small as compared with surface energy. It meant that force could only be exerted for about a 25o-millionth of an inch or a distance

of that order to give the small surface energy that is observed. It was forgotten for a hundred years. Nobody paid any attention to it till Rayleigh called attention to it in 1899. I started to work, in the General Electric laboratory in 1909, on high vacuum phenomena in tungsten filament lamps and began introducing different gases into the bulb to see what would happen, just to satisfy my curiosity. There was no particular problem to be solved, but I simply found there was a great opportunity there to do things that nobody else had ever been able to do before. So I tried a lot of things. I put nitrogen, hydrogen and oxygen into a bulb and heated the filament to 3000 degrees Centigrade and I found very soon that some very extraordinary things happened. One was that oxygen formed into a film on the surface of the filament. It was held so tenaciously that it could stand heating up to 1500 degrees absolute for years, and you could not reduce it with hydrogen. It would not react with hydrogen. There was a degree of force holding the oxygen and giving it entirely different properties from oxygen in bulk. I became convinced that there was a direct chemical union between oxygen atoms and the underlying tungsten. After the oxygen atoms were once combined with the tungsten atoms you could not expect other atoms to combine with the oxygen. When I ran upon such a phenomenon as that, I automatically adopted the viewpoint of the chemist. Let us go back to see what the C 29 ]

differences in the approach of the chemist and the physicist are on these matters. The physicists have a long history of the study of forces subsequent to the discovery of gravitation, following Newton. They studied the electric forces and the magnetic forces, and they thought of forces in terms of the square of the distance, and so on. They were familar with forces of very long range, and would think of gravitation acting between here and the sun. The chemists, on the other hand, while seeking where the field particularly was, came into contact with atoms and molecules. The chemists took for granted that one molecule acted upon another when one came in contact with another. That was obvious. You could not expect a hydrogen atom to combine with an oxygen atom unless there was contact between them. You did not need to think of any explanation of it. It was simply obvious. So the whole method of approach was different. The chemist was inclined to think of contact as being the important thing, and the physicist was looking upon this as some sort of interaction. So when they came to study surface tension phenomena, the physicists said, "Well, let us assume that molecules are spheres and that they exert force on one another and that this force is some power of distance, as between the earth and the sun." That was the method of approach. Physicists were the only ones studying surface tension. So, on the whole, surface tension was worked out that way - on the basis of long-range forces. However, the phenomena that I came across, more or less accidentally, were forces that the chemists were CSo]

dealing with. I thought of tungsten coming in contact with the oxygen atom and saturating it just as definitely as oxygen atoms are saturated when they combine with two atoms of hydrogen. They will not take up any more. So the approach of the chemist is different from that of the physicist. There is not any fundamental difference, but just one of tradition. I think that all the success that I had in dealing with surface forces was due, more than anything else, to the fact that I brought out a new method of attack on surface tension forces. I took it for granted that the forces between molecules and atoms were short-range forces, unless the contrary was proved. I know there are plenty of surfaces charged with ions, for instance, which exert force on one another. If I have a charged sphere here, it will react on another charged sphere over there. I like to forget about the exceptions and deal with ordinary cases and see how far we can go. We can go an awfully long way with surface phenomena just by thinking only of what happens when the molecules on the surface are in contact. With regard to chemists, for a long period of time before 1920, they thought of molecules in terms of structures as is shown by the structural formulas of organic compounds, graphic formulas. The organic chemist in early work believed that there was a structure; although, when he put a bond down he did not think it was a piece of steel holding atoms together. It was a symbol for some sort of force, but he was very sure that the linear sequence of the atoms was what he found it to be in his formula.

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Then about 1900, Ostwald's studies led him to believe that this was all hypothetical. He even wrote a chemistry book for high schools in which the atoms or molecules were never even mentioned because, he said, it is very harmful to have unnecessary hypotheses. Let us have facts. The facts were all kinds of experimental data. He would not think of atoms and molecules, because they were absolutely unproved and unprovable hypotheses. He changed his mind later on when he saw and heard of Perrin's work and particularly when he saw a spinthariscope in which you could see the single atoms as they struck. However, the teaching between 1900 and 1910 in the field of physical chemistry was that atoms and molecules did not exist and, if they did, they were just hypotheses. They were nothing but fiction and were as indefinite as fiction usually is. You could make of it anything you wanted to. Only ten years or so before, J . J . Thomson had begun to work with individual electrons. Then came radioactive phenomena. Physicists were now approaching the point where they were absolutely sure that there were atoms and molecules. That did not have any effect on the chemists. They still kept on believing it was nothing but fiction. I became convinced when I started in, that the proof was conclusive that atoms and molecules were perfectly real things. Then I said, if that is so, go the whole limit in treating this idea. Let us take all of the consequences. The atoms and molecules must have shapes, sizes, positions, and all the rest of the properties that go with them. That is to be expected. One is going to expect the C 32 3

old lock-and-key theory of the fitting together of biological bodies, for instance, in molecules - which was proposed, I think, by Fischer and long ridiculed by Ostwald. This theory seemed to be a perfectly rational interpretation of interactions and specific reactions between bodies, and its acceptance nowadays has led us to build new theories. I shall not stop any longer to talk about the work that I did on reactions in gases, except to say that with tungsten filaments, having found this example of oxygen holding so firmly, I found several other situations of a similar kind. I found that a single layer of thorium atoms on tungsten could increase the electron emission from a tungsten filament in vacuum ioo,ooo-fold. That was very important from a technical point of view, as thousands of millions of radio tubes were made having filaments of that kind. However, if my viewpoint was right, it ought to have a wider field of application. It ought to apply, for instance, to surface tension phenomena for liquids. So, the first time I began to consider those, I read literature by Bredig, Deveaux, and a few others. I adopted this point of view: that the organic molecule has, of course, a structure as the organic chemist said it had. That is what the organic chemist found it to be, and he had a good reason to think so. If that is true, and contacts are the important thing, what would happen if you brought that molecule in contact with water? The carboxyl group would cause the molecule to dissolve in water; as acetic acid, which is mostly a carboxyl group, dissolves in water. The other C 33 U

hydrocarbon portion of the molecule, which will not dissolve in water, therefore stays on the surface. So before I made the first experiment, I expected, from the mere idea of short-range forces acting between different portions of molecules that were in contact, that the forces originated from atoms rather than from molecules as the whole. You are automatically led to think of several results. First, that if you have single layers of molecules, they will be oriented and held on by specific chemical interactions between groups of atoms in this substance and the underlying water, and that if you had a substance with molecules that did not have any group attracted to water, they just would not spread. That is exactly what we found. Hardy had observed that before, and associated it with the lack of chemical action, but he had no definite theory. He had the idea that the range of forces was of the order of hundreds of molecular diameters, a very long range; therefore, he thought that if there were any orientation in the layer, it was many molecular layers deep, which is quite a different theory and does not lead to any agreement with the experience that we found. Just to picture the thing qualitatively, suppose you have a molecule which is a long hydrocarbon chain with carbon atoms in it and with a group on the end that has affinity for water, and you bring the molecule into contact with water. The end tends to go into the water, and the hydrocarbon chains tend to stick to each other, because hydrocarbons do stick to one another; that is, they don't vaporize at ordinary temperatures, which C 34 3

proves that they stick together. You thus have the whole surface covered with these molecules side by side. When spread over a limited water surface, what could be more obvious than to say that a second layer cannot form, because the second layer cannot come into contact with the water. That is sort of chemical common sense. When one molecule fills the space there is no space for any more. You arrive at the idea of saturation, which did not occur to the scientists dealing with the problem. If you have a pure hydrocarbon without these groups, for example, petrolatum or Nujol, it forms little globules on the surface of the water. You drop them on the water and they stay where they fall. They do not spread out over the surface of the water. But if you put into that pure hydrocarbon one part in 100,000 of olive oil, you will see it gradually beginning to spread, because all the olive oil molecules that have active groups occupy the surface at intervals and they compete with one another. They all move around and they gradually occupy places and squeeze against one another and spread the film out until it becomes so thin that every molecule of the added substance has a place on the water. We tried some simple experiments to test these ideas. First of all, it seemed worth while to make some measurements of these forces. Figure 1 shows the apparatus that we used. T was a trough, just a photographic tray, containing water. In the early experiments paper strips, A and C, were used to compress the film. Nowadays the trough is filled with water to the brim, and metal barriers resting on the two edges are used instead of the C 35 3

FIGURE I .

Diagram of trough used in early experiments, showing surface pressure balance.

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paper strips. B was a movable barrier made of paper or metal foil, attached to the two legs R R' of the balance. F and F' were jets of compressed air to keep the oil film from passing from one side of B to the other, but instead of the jets you could use a thread. We put a minute amount of oil on the water surface at O. The oil spread out over the surface in a film about one-tenmillionth of a centimeter in thickness. As the film spread it pushed against the barriers. We applied weights to the pan P of the surface balance to measure the force. That force was a differential surface tension measure. It measured directly the "spreading force." We looked upon the phenomenon of a spreading force just as you would a gas striking against a piston. The water surface was like a cylinder, with the barrier A serving as a piston, and the oil that was spread on the water was like a gas filling a cylinder. If the oil were a two-dimensional gas, the force measured by the surface balance would be the measure of the pressure. That is the type of measurement that we started to make. We changed the area by moving the barrier A and compressing the film, and measured the force by holding B at a fixed point against the pointer, J by applying weights to the balance. What we really did was to put a large weight on the pan which moved B past J, and then we moved A until the compression of the film restored B to the equilibrium position J. Then we put on a stronger weight and compressed the film still further. To buy an outfit like that would cost a couple of hundred dollars. This outfit was made in one afternoon. Of

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course, if you want greater accuracy it would pay to use better apparatus. We think it can be done with things that you can make at home. Figure a is a graph of the kind of results that we obtained. The surface force was plotted against the area per molecule of oil. The force on the water surface was measured in dynes per centimeter. We divided the total area covered by the oil by the amount of material in the film. We knew the molecular weights of these substances, so we could calculate the area per molecule. Along the line OX there was zero force. Under those conditions the film spread out, not indefinitely, but to a very large area. Then, as we began to compress it at certain points, it exerted a certain force. This diagram is not a diagram of any particular substance. If you measure the fatty acids, you obtain points along a line BH, a practically vertical steep line up to a certain point, and then the film collapses or crumples up. Along BH the film is very difficult to compress. It is called a condensed film and is either solid or liquid. I do not think there is any strict definition of what we mean by that. Practically, what I mean by it is whether it is mobile; for instance, if you put. a little piece of paper on the film and try to blow it, you may find the paper will not move. I t is just as if the paper were frozen in a cake of ice. You say the film is solid. On the other hand, if you can rotate the paper without trouble, even if the film is under pressure, you call the film liquid. Actually the force that is needed to make the paper rotate is the measure of viscosity and, possibly, rigidity.

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Area FIGURE 2.

per

molecule

a

Force-Area Diagram.

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I am thinking of the molecules on the water as real objects. You see, the moment you start to draw a picture of them, as the organic chemist does, you think of them as having shapes, lengths, volumes. It is true that you have rotation, a bond between carbon and carbon. Therefore, these chains of hydrocarbons are not to be looked on as rigid and inflexible chains but as pieces of ordinary iron anchor chain. The molecule has a maximum length, but it has no particular minimum length. I t can assume different shapes, in which the carbon atoms always have a linear sequence. Therefore, when you compress the film to its smallest area the chains must have their maximum length; in other words, they must be arranged so that the hydrocarbon atoms are vertical. The molecules will then occupy their smallest area; and a measure of that area enables you to calculate the cross section of the molecules when they are squeezed together and extended to maximum length. Under those conditions, what do you expect? Well, first of all, when you increase the length of the chain by spreading a film composed of molecules having a longer hydrocarbon chain this will not change the area of the film, but will change its thickness. Volume divided by the area is the thickness, so you can calculate the thickness. Total area divided by the number of molecules is the area covered by each molecule. You know right away the dimensions of the molecule, that is, how the cross section area compares with the length. Then, if you remove the force - let the film expand in some cases - you find that these films now extend to much bigger areas, which means that the molecules have C 4° ]

slumped down and they are like a liquid. Just as in a liquid the chains would not be piled up regularly on one another, so in the case of the films they can be irregularly arranged, still sticking together, but having a surface tension force. Y o u have then what we call an expanded film in which the tails of the molecules simply form a little liquid, a little bit of a liquid volume. It may be much less in thickness than the length of the molecule; and yet, our experiments have shown that it really behaves as a real liquid, bounded by an upper surface and a lower surface. In Figure 2 the curve H R J K refers to a film which is a single molecule thick; and yet the film has three parts, two interfaces and an interstratum. The interstratum is essentially a liquid in bulk, and one of the interfaces is a two-dimensional gas. That theory of the state of the film can be worked out practically quantitatively for the study of a whole class of films that are called expanded films, such as olive oil or oleic acid. All form gaseous films at low pressures; and yet they differ from a gas in that instead of giving an ordinary hyperbola they give a hyperbola J K whose asymptote S T comes below the zero point on the force axis because of the force of attraction between the molecules. Because of the constant tension of this force the film has to have a certain amount of spreading force SO, before you can begin to measure the spreading force, because it is counteracted by the tendency of the whole film to contract. I would like you to believe in the reality of these concepts. I like to think of the concreteness of them. Apply C4i 1

ordinary everyday laws of reality to molecules so that you can picture their behavior. Of course, there may be some discrepancies, but still carry those ideas as far as you can. For example, you can use them to reason that the top surface of the film must be just about as smooth as any liquid is. There will not be any molecules sticking up because molecules of a hydrocarbon do not evaporate from one another. If a molecule should be surrounded by air, it would be in about the same condition as when evaporated. Therefore, the molecules will not be in an empty space. They will be stuck down together with a relatively smooth upper surface because the tension forces between the molecules tend to make the surface area minimum, for the same reason that liquid in bulk tends to a minimum surface. Figure 3 shows how you can make a film which is i o - 7 centimeters thick "visible" by marking its boundaries. For this purpose you need some automobile oil. Y o u can use oil taken from an automobile crankcase. T h e more the oil is oxidized the better it is for this purpose; in other words, if you want to use fresh automobile oil, heat it in an oven or on a hot plate until it almost catches on fire, and stir it and let it become badly oxidized. If you put a drop of this oil on water, it will spread out into a film which reflects beautiful iridescent colors. It may be red, green or blue, or other color, depending on the amount of oxidation. If you compress it between barriers, it will change color because it changes thickness. W e call that the indicator film. Figure 3 shows the surface of water in a trough. This C42 3

FIGURE 3 .

Expansion Pattern of Pepsin.

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trough is about six inches wide, and the bottom of it is painted black. We first put some indicator oil on the water which spreads in the film O. That reflects a great deal of light compared with the black bottom of the trough. Then we take a very minute fragment of crystalline pepsin, or any kind of solid pepsin, a piece about like the smallest grain of sand, maybe a thirtieth of a cubic millimeter in size. We just stick this little fragment on the end of a platinum wire and touch it to the surface of the water and immediately the black area P appears. The molecular layer of pepsin has displaced the indicator film in the area P, and therefore you see the black bottom of the trough through the clear water surface. You see the location of the pepsin film as a black area and therefore you can say that you "see" the film. Of course, the film is only i X i o - 7 centimeters thick, and is actually entirely invisible. Pepsin spreads into a certain circular pattern. Y o u wait a minute or two and then in the center of it you put another drop of indicator oil, and now the oil spreads to form a star-like design O', not a circle. Pepsin is the only substance that I know of, which gives that particular shape or pattern, i o - 7 grams will cover a square centimeter, which will be enough to make a test of this sort. Figure 4 shows samples of other proteins. Wheat gliadin shows a star-shaped figure. With egg albumin the outside edge is an irregular line and the inside edge is irregular. With insulin you get a smooth line, both on the inside and on the outside. The expansion patterns in Figure 4 show the points of C44 3

FIGURE 4.

Expansion Patterns of Proteins.

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difference in proteins. Some of them are solid or plastic bodies. They tear, as a piece of leather tears as it is expanded. Others form liquid films that expand with a smooth boundary. It is interesting to use the method of expansion patterns to study some of the changes in proteins; for instance, the biologist knows that proteins are very specific substances having definite biological reactions, definite molecular weights, and they are easily denatured or changed so that they lose their specific biological properties. One way to denature them is to heat them. In our tests we heated some pepsin for two minutes at 65° C. We tested biological activity and it was still unchanged. After five minutes at 65° the activity was reduced to 70 per cent. We tested the expansion patterns and found that the star-like shapes were already beginning to change. The corners were not so sharp. After seven minutes at 65°, the activity was not much decreased, but the pattern of the film was becoming circular. Twenty-five minutes at 65° caused a 60 per cent decrease in activity. Now the film had become completely liquid and there was no tendency to form star-like patterns. So by this very simple procedure you can follow chemical changes in molecules. One interesting thing about it is this: some people say that when a protein is spread it is denatured, and some people say that there is only one kind of denaturation. Expansion patterns show right away that the denaturation by spreading is different from the denaturation by heating, because a film that has not been heated gives C46 3

a star-like pattern, but if you heat it before you spread it a star-like pattern is not formed. Therefore you have an indication that the change that is produced by heat is certainly not the same as the change produced by spreading. We made two other tests of denaturation. We irradiated pepsin for ten minutes and it still retained 96 per cent of its activity, but there was a very big change in the film. Again the effect of irradiation for thirty minutes was different from the effect of irradiation for ten minutes. If the protein was shaken 400 times, it formed a liquid film. After being shaken 4000 times very little of the pepsin would spread on the water surface. Spreading is an unfolding, let us say, of the molecule, but shaking does two things: it forms new surfaces, but after shaking a few hundred times you are not only forming new bubbles, but you are breaking old bubbles. The total number of bubbles does not increase. Every time you are breaking bubbles, you are crushing your molecular layer and you have resulting changes in its character. The tests show that shaking produces a different result from spreading. You can call them both surface denaturation, if you like, but there are two different mechanisms involved, and they have different effects; that is, the shaking gives a liquid expansion pattern whereas the spreading gives a star-shaped pattern. I do not know the significance of these things. They are of significance to somebody who is working with proteins and particularly somebody who is trying to use the C47 ]

phenomena of denaturation in the study of the structure of proteins, because in most of our knowledge of the structure of proteins the whole polypeptide theory of protein structure is based on the study of degradation. When you hydrolyze this polypeptide chain by boiling, it certainly denatures it more. I t breaks it down as a polypeptide chain. From that you learn what the structure is, and you can say that the structure must be a polypeptide chain. The method of expansion patterns has been very successful in giving us a lot of knowledge. It seems to me it will be very important to take these minor forms of denaturation and try to distinguish them first qualitatively and then make quantitative experiments. However, more than that, what do these experiments mean ? We measure areas, we measure viscosities, and I am going to describe more properties we can measure; and these properties that we measure are directly related to the forces between different parts of the molecular structure. I shall describe some other different methods of studying monolayers. First, there is a technique which we have found available for measuring the thickness of protein layers. This is done by depositing films of these substances onto plates which are specially prepared. You can build up multilayers by the very simple technique of taking a plate of metal or glass and dipping it down into water on which a suitable film is spread and pressure is maintained. As you lift it out, it comes out with a layer on it. If you push it down again, you get another layer on it, and every time you go either down C48 3

or up with certain kinds of substances you get another layer, until you build up films that you can see. The substance most commonly used for building multilayers by this method is barium stearate. It is prepared by spreading stearic acid on the surface of water containing a small amount of a dissolved barium salt. The thickness per layer is 24.4 Angstroms. If you build up films in this way to a thickness comparable to a quarter wave-length of light, you find that any additional change in thickness produces an enormous effect in the reflected light, so that optically you can see differences of thickness as little as 1 Angstrom. Figure 5 is a graph of the intensity of monochromatic light reflected from a film built of multilayers of barium stearate on polished chromium. The film was built in steps having 4 1 , 43, 45 layers. It was illuminated by sodium light, polarized with the plane of polarization perpendicular to the plane of incidence, and directed at the film at an angle of incidence, i = 8o°. The circles on the graph show the intensity of light reflected by the steps A, B and C having 47, 49 and 51 monolayers. Step B reflected so much less light than the neighboring steps A and C that it appeared nearly black by contrast. A film of this type, built in a series of steps, can be used to measure very accurately the thickness of a protein monolayer. The plate having the step-series is lowered into water on which a protein film is spread, and as the plate is withdrawn the protein film adheres to the top of the multilayers. In Figure 5 the crosses on the graph represent the intensity of reflected light after a protein monolayer having the thickness of 20 A.U. C49 3

X

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4!

43

45

47

49

5/

53

55

57

NUMBER OF LAYERS FIGURE 5. Intensity minimum for step-series of monolayers of barium stearate, built on polished chromium. Films seen by polarized ray Rs of sodium light at an angle of incidence i = 8o°. HOHOLAtCR VISCOSITY Y

FIGURE 6. Monolayer Insulin.

Viscosity.

FIGURE 7 (facing). Protein Mono layer Viscosity. F= 10 Dynes I cm

mord» MOWH-tn» vitcosrrr T n o dthi/ch

has been added to a step-series. The change in contrast of the steps A, B and C is very great. It is possible by using suitable optical means to measure the changes of intensity corresponding to changes of thickness of i A.U. In other words, you can detect differences of layers corresponding to atoms in thickness. Another way in which proteins can be studied is by measuring the viscosity of a monolayer on a water surface. The procedure is very simple. A small torsion apparatus is made by suspending a horizontal disc of metal one inch in diameter by a wire, such as a 3-mil tungsten wire. The wire is mounted on a little cork which rests on a support above the trough and can be turned so as to rotate the disc. You lower the apparatus until the disc just touches the surface of the water, spread a film on the water, and put the film under certain compression. You find, as you compress it, that the disc is damped in its motion or maybe will not rotate at all. You may be able to turn the cork through 90° and the disc does not follow. The graph in Figure 6 shows measurements of the amplitude of successive swings of the disc. The measurements were made for an insulin film at pressures of 1 dynes, 6 dynes and 10 dynes per centimeter. As the pressure was increased the film became much more viscous and the slope of the line served as a quantitative measure of the viscosity. Figure 7 shows data on a whole series of proteins, all at a force 1 dynes per centimeter: gliadin, zein, casein, gliadin acetate, insulin, tobacco seed globulin, papain, haemoglobin, egg albumin, trypsin, trypsinogen, pepC 51 n

sinogen, pepsin, edestin, horse globulin. Y o u see what an enormous range you obtain with different proteins. The graph shows that the last five proteins in this list did not permit the disc to swing at all. Different proteins have different characteristics which certainly must be related to the forces of interaction between the molecules. A second way of measuring the viscosity is to use the aperiodic method. This is used to measure the films which did not permit the disc to swing in the first method. In that case you turn the disc 90° and, although it will not swing, it will gradually return and the rate of return can be measured. With the horse glubulin, you notice that when you turn the torsion head 90° there is a yielding by the film of about 3 0 , and from that time the disc is held motionless. The horse globulin is a rigid film, that is, it is a solid body. See Figure 8. Some of the protein films are very sensitive to pressure. Casein, for instance, when compressed at 16 dynes gives a curve which is enormously different from the curve obtained at 19 dynes. This difference is not obtained with other proteins. A great many kinds of characteristic behavior of proteins can be observed by means of this tool, which could not be measured in any other way, since the amount of substance in a monolayer is exceedingly minute. Figure 9 shows a phenomenon which we found with some of the proteins. P is a film of trypsin surrounded by indicator oil O. O' is indicator oil spread in the middle of the trypsin. The ring at the edge of O' which C 52 3

F s 10 D Y N E S / C M . APERIODIC METHOD

®H-®D

100 F I G U R E 8.

TIME

SECONDS

Aperiodic Method. F = io

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Dynes/cm.

200

F I G U R E 9.

Trypsin Monolayer Showing Edge Effect.

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appears light in the photograph was actually many colored. The colors depended on the thickness of the film and indicated that the film became thinner at the point where the colors appeared. We suspected that that was due to some impurity in the trypsin. It might have been a soluble product that was reduced by the changes that took place as a result of spreading; in other words, when the protein spread there may have been some low molecular weight products that formed as by-products. I do not know. However, in general we have found that the purer the product the less tendency there was to get the edge effect. This trypsin was obtained from Northrop and was given to us as a very pure crystalline trypsin. We think the color changes occurred because some soluble product from the protein went into solution in the water and subsequently diffused up to the lowest surface of the indicator oil and became absorbed, causing the oil to spread out to a thinner film. We proved that that was correct by a whole series of experiments specially made. We were able to spread these protein films on the water, scrape the proteins off after holding them under pressure, and then put indicator oil on the water and watch the change in the area of the oil. The area did change and the color changed. The area increased, showing that the amount of substance that entered the oil was about the same amount of substance that disappeared from the protein film when it was compressed. Figure 10 shows typical force area data obtained with a pepsin monolayer. The protein film was compressed with a definite time sequence t 55 3

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at each point, taking the readings at one minute after each successive pressure was applied. If you increase the pressure up to some point like B at 25 dynes and hold the pressure constant for a time until the area contracts from B to C, and if then you decrease the pressure, the readings do not come back along the same curve, but follow some curve such as CD. When you go up again they then follow D E , and when you come down they return to D. You can repeat it as often as you want, but you will never get back to the point A. In other words, the first time you compress the films some substance is lost permanently and the difference between D and A is a measure of the amount lost. It is some soluble product in the protein, either an impurity or something formed by the spreading; and after it has been removed you can repeat the compression and expansion over and over again with the same film without further change. The contraction of the film from E to C when the pressure is held at 25 dynes is not due to the compressibility of the film. I t is due to the rearrangeability. You are pushing out of the film, parts for which there is no room, which go into folds in the underlying water and are not lost to the film. They are displaced, so that they are hanging in folds underneath the surface. After this process has taken place, it takes time for these less hydrophobic parts to come back again into the film. However, they do come back. This is what is happening along a line such as G H on Figure 10. After holding the pressure constant at 25 dynes for a few minutes, the pressure was lowered to 18 dynes. It was held at that C 57 3

FIGURE I I .

Force-Area Time Curve for Various Proteins.

value and the film expanded from G to H, as the parts which had been displaced returned to the surface. Figure 11 shows a series of curves that were obtained at a definite time sequence, taking points with one minute intervals on the way up. Notice that the curves for pepsin, trypsinogen, egg albumin, wheat gliadin and insulin are very different. We have worked out and published a report that seems to correlate these changes exactly or very accurately within the accuracy with which the analyses are known, with the composition of the protein; in other words, these proteins that will stand a lot of pressure will stand the pressure because there are some hydrophobic groups of particular size and length, which are hard to force away from the surC58H

face. Insulin contains a lot of leucine, which is very hydrophobic. Wheat gliadin has predominantly hydrophilic groups. Therefore, it is much easier to stretch or squeeze the groups of wheat gliadin from the surface. Figure 12 shows the tremendous effect we get by heating pepsin. A is the curve for native pepsin. After pepsin has been heated for ten minutes at 65° the compression follows curve B and the film shrinks to 25 per cent of its area. When the pressure is released only 40 per

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cent of the original area is recovered. Therefore, some part of the pepsin has been rendered soluble by heat, and that goes into solution in the water. From these data we have worked out a theory, and we can calculate that the molecular weights of those products that are formed by heat denaturation are of the order of 2000; the protein itself is somewhere around 35,000. With regard to the structure of proteins, the work with surface films does not, of course, tell us the structure of proteins, but it tells us this very definitely I think: that in spreading a protein you change the shape of the molecule from that of the globular protein, which is approximately 25 or 30 Angstroms in diameter, to something which is perhaps a quarter of that or less, 8 or 10 Angstroms in thickness, which means that the original shape has been broken down. You cannot very well tell what it was originally, but you do know this: that the cause of spreading must be the presence of hydrophobic groups. The proteins themselves, like insulin and egg albumin, are highly soluble in water. The films are completely insoluble in water. You cannot get them back into solution by compressing them or, in fact, as far as I know, in any way, unless you degrade them still further. That difference is best accounted for by saying that in the proteins themselves the hydrophobic groups, which are present in the side chains, are buried in the interior of the molecule and that, in the spreading process, those are brought to the surface, and it is the presence of those hydrophobic groups that cause the spreading phenomena. C

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I think, in general, the best picture of this structure is Dr. Wrinch's theory of the cyclol structure. A great deal of work has been done recently on the question whether monolayers of proteins, that is, films spread from solution of the proteins and then deposited on plates, for example, retain their biological activity. We worked with pepsin and we found that it still could clot milk with full activity, apparently, after it had been spread. I t does not do it by acting while it is on the plate. What happens is this: you deposit a single layer of pepsin on a glass plate or metal plate, put that in milk and immediately the pepsin that was on the plate goes into the bulk of the milk and will continue to clot the milk after you take the plate out. Therefore, it has gone from the plate; in fact, if you dip a plate covered with a monolayer of protein for two or three seconds in some milk and then put the plate in a second batch of milk, the second batch of milk will not clot and the first milk clots about twenty minutes after the plate has been removed. The experiment proves that in that case the monolayer is active or converted into something that is active by something in the milk. I do not know which it is. Dr. Rothen and others at the Rockefeller Institute have been recently making some very interesting experiments, and I have a reprint of a paper of a symposium that they are publishing, in which they find that insulin is fully active after having been spread in a monolayer, although its thickness is a third of the thickness of the insulin molecule. These are cases where monolayers retain their activity. On the other hand in sev-

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eral other cases that they studied, the activity was completely lost. However, the antigenic properties of egg albumin, for example, are retained after the monolayer has been spread. After such studies as these I should suggest making experiments to find out whether the activity is modified by putting the film onto the glass at different pressures. We found considerable difference in the case of pepsin ; that is, if the film was put on the glass under high pressure, its activity was damaged very much less. So, although you will not be able to work out a theory of structure directly from these measurements, it does seem as though you would be led to clues of structure that could be confirmed by experiments. The rapidity with which you can study phenomena is extremely great because of the simplicity of the method.

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Nuclear Physics and Biology E R N E S T O.

LAWRENCE

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N E might argue that physics plays a comparatively minor role in the life sciences, for a biologist is usually well-trained in chemistry, while often his knowledge of physics amounts to hardly more than what he learns incidentally in chemistry. He frequently uses a microscope without a knowledge of optics and an X-ray machine without an understanding of X-rays, and he is rarely curious about the physics of living things. Now there are signs that this picture is changing. There are indications of a new epoch wherein the physicist is to close ranks with the chemist and the biologist in the attack on problems of the life processes. I should like to take this opportunity to discuss some of the recent notable advances in nuclear physics that are finding wide application in the biological sciences. Radioactivity and A t o m i c Structure T o introduce this subject, may I recall that Rutherford came forward in 1904 with a revolutionary hypothesis which reduced the complicated and mysterious observations of radioactivity to simple order. He suggested that not all of the atoms have existed for ages C63 3

and will exist for all time, but there are some atoms in nature that are energetically unstable and in the course of time spontaneously blow up with explosive violence. These are the natural radioactive substances, and the fragments given off in the atomic explosions are the observed penetrating rays. Nowadays the ideas of Rutherford and Bohr on the structure of atoms are firmly established. There is an abundance of evidence that an atom consists of a nebulous cloud of planetary electrons whirling about a very dense sun - a positively charged nucleus - and that it is in the nucleus that the atomic explosions of radioactivity occur. The nucleus consists of a closely packed group of neutrons and protons - elementary building blocks of nature some two thousand times heavier than the electrons - so that the nucleus contains practically all of the atom's matter and, indeed, energy, because matter is one form of energy. The protons and neutrons are visualized as extremely small, dense spheres of matter, so small indeed that, if an atom were as large as a cathedral, on the same scale the nucleus of the atom would be no larger than a fly! The protons carry positive charges of electricity, and the number of protons in the nucleus equals the number of planetary electrons because the atom as a whole is electrically uncharged. In other words, the nucleus of an atom contains a number of protons equal to its atomic number. Neutrons, on the other hand, are electrically uncharged, and accordingly the number of neutrons in the nucleus does not affect the planetary electrons. Varying the number of neutrons in the nucleus only alters the weight of the C64]

atom. Thus it is that we have isotopes oi the elements atoms of the same atomic number but different weights. Nuclear Transformations This is enough of an account of atomic structure for our present purposes. We see that the age-old problem of alchemy - the transformation of one element into another - is simply the problem of changing the number of protons in the nucleus, while we may produce isotopes of the elements by adding or subtracting neutrons. Because the nuclear particles are so dense and so firmly packed together, the problem of bringing about such nuclear transformations on an extensive scale was early recognized as essentially a technical problem of producing swiftly moving nuclear particles - protons, neutrons, deuterons (heavy hydrogen nuclei) and alphaparticles (helium nuclei) for bombardment purposes; for it appeared that the only feasible way to knock in or knock out protons from atomic nuclei was to smash them with projectiles of similar density. Accordingly, laboratories over the world have been engaged in the development of various sorts of atomic artillery. Among these the cyclotron has proved to be particularly useful. In the cyclotron ions are generated at the center of a vacuum chamber between the poles of a large electromagnet and spiral on ever-widening circular paths to the periphery under the combined action of a radiofrequency oscillating electric field and a steady magnetic field. The circulating ions resonate with the oscillating electric field, and the magnetic field serves to C65 3

balance the centrifugal force of the ions as they circulate. In this way the medical cyclotron in Berkeley (Figure i*) regularly produces 16 million electron-volt deuterons or 32. million electron-volt alpha-particles. Usually the beam of swiftly moving ions reaching the periphery of the chamber is directed against a target, but on occasions the beam is allowed to emerge into the air through a thin metal plate, and in Figure 1 such a beam of 16 million electron-volt deuterons is seen to produce a lavender luminosity for a distance of feet. The beam in the air looks rather pretty, but its appearance hardly suggests its latent powers. However, some conception of the energy in the beam is gained when a steel plate is placed in the path of the beam, for it is immediately melted and cut through - a rather fancy substitute for an oxyacetylene torch! A much more subtle danger, moreover, lurks in it because, as the swiftly moving particles lose their energy, they make nuclear collisions giving rise to penetrating nuclear radiations - the gamma-rays and neutron rays, which like X-rays produce harmful and even lethal effects in excessive doses. I t is for this reason that the cyclotron is so carefully surrounded by large masses of absorbing material to protect the operators (Figure 3). Biological Action of Neutron Rays I suppose that almost as soon as he had discovered the neutron, Chadwick wondered about the biological action of neutron rays. I know that in Berkeley, as soon • All illustrations referred to in this article appear together following page 95.

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as we observed that neutron rays were coming from the cyclotron, in some abundance, we were curious as to what biological effects they would produce - particularly on us! I t was extraordinarily fortunate that my brother, Dr. John Lawrence, was visiting our laboratory the first summer we had neutron rays from the cyclotron in sufficient intensities to warrant investigating the question. He gave up his vacation to look into the matter, and in his first experiments he observed that neutrons were exceedingly lethal. Perhaps one might think it presumptuous to have an opinion on such a matter before experimental observations were made, but we did suspect that neutrons in comparison with X-rays would produce quite different biological effects, for neutrons were known to produce a vastly different distribution of ionization in matter. This is shown in the cloud chamber photograph of ionization produced by a mixture of X-rays and neutron rays (Figure 4). The X-ray ionization is produced by secondary electrons, which are responsible for the thin tracks and the generally diffuse ionization shown in the photograph, while the neutrons produce ionization by making nuclear collisions and causing nuclei to recoil. The resultant ionization paths of the recoil nuclei are from a hundred to a thousand times more intense than those of the secondary electrons. If one were to indulge in an analogy, one might say that X-ray ionization resembles a San Francisco fog, while neutrons produce a shower of droplets, like a good New Brunswick rain! In particular, a simple calculation will show that X-rays would rarely ionize two parts of a single protein molecule C67 3

while neutrons will often produce double ionization of such a large molecule. This fact alone would lead one to suspect that neutrons might produce quite different biological effects. A great deal of work has been done in recent years following the first experiments of my brother, and there is an abundance of evidence now that neutron rays do indeed produce qualitatively different biological effects. I should like to take this occasion to speak very briefly of some very recent work along this line by Dr. Alfred Marshak. As is well known, irradiation of cells with X-rays produces chromosome abnormalities, and in particular it is observed that X-rays produce chromosome fragmentation. That is to say, when some irradiated cells go through mitosis, the separating chromosomes are observed to split off one or more fragments which are isolated from the cell nucleus (Figure 5). Dr. Marshak has studied this X-ray fragmentation very extensively and has obtained significant and fundamental information on the effects of ionization in cells. Recently he has been studying the chromosome effects produced by neutrons with the results shown in Figures 6 and 7. Such curves give us a quantitative measure of the sensitivity of chromosomes to X-rays. The steeper the slope the more susceptible are the chromosomes to damage by X-rays. Similar curves are obtained when tissues are treated with neutrons. The ratio of the slope for neutrons is a measure of the relative efficiency of neutrons and X-rays in producing damage to chromosomes. It has been found that this ratio is 2.5 for chromosomes irradiated at the onset of the nucleur prophase. When C

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irradiated in the resting stage, however, the ratio rises as high as 6. Thus, neutrons are more efficient than X-rays in producing damage to cells in the resting stage. Neutrons, therefore, produce different qualitative as well as quantitative effects on chromosomes. Since many of the tumors which do not respond to X-rays do not undergo mitosis frequently, i.e., have a much greater proportion of their cells in the resting stage, it seems quite likely from these results that such tumors may regress when treated with neutrons even though they are resistant to X-rays. Neutron Therapy This being the case, the clinician is immediately interested in the possibility that these qualitative differences might be used to advantage in therapy - particularly in the treatment of cancer - for, as you know, there are some tumors that respond very well to treatment with X-rays or radium. Some cancer cells seem to be killed more readily by the effects of radiation than the normal cells, and such are called radiation sensitive cells. There are unfortunately a large class of malignancies that are more or less radiation resistant which do not respond satisfactorily to radiation therapy, and it becomes a problem of great importance to determine whether at least some of these tumors not successfully treated with X-rays might respond to neutrons. Although a considerable number of animal experiments on this point were encouraging, the only real answer was to be found by trying neutron therapy

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clinically, and, accordingly, a program of clinical investigation was begun two years ago under the active direction of Dr. R . S. Stone, Professor of Radiology in the University of California Medical School, who has had extensive experience with cancer therapy, using 200,000 volt and 1,000,000 volt x-rays, and Dr. J . C. Larkin, who has devoted his full time and efforts to all sides of the clinical problem. For the clinical work it was necessary to have a welldefined beam of neutrons in order to irradiate tumors in human beings locally just as is done with X-rays. From our brief résumé of nuclear structure, one can see that neutrons are knocked out of nuclei under bombardment and it happens that a most prolific emission of neutrons is obtained from a target of beryllium metal bombarded by deuterons in the cyclotron. The nuclear reaction is shown in Figure 8, and it is seen that it is one wherein the beryllium nucleus is transformed into a boron nucleus by capture of the deuteron and emission of a neutron. The neutrons come out in all directions from the beryllium target of the cyclotron; and, in order to produce a beam, the target is surrounded by a thick screen with a channel through it. The screen is about 4 feet thick and consists of paraffin, boron and lead to absorb both neutrons and gamma-rays from the cyclotron, except the radiation through the channel from which a neutron beam of desired cross section emerges. The orifice from which the neutron beam emerges is called the treatment "port" and is shown in Figure 9. I t is in the wall of a treatment room, and, as far as the clinician or patient is concerned, the arrangement for

neutron therapy is just the same as for deep X-ray therapy. Of course preliminary to the beginning of clinical work a great many animals were irradiated with the neutron beam in order to have further biological measures of the dosage. For example, the minimum neutron dosage which would remove hair from a rabbit was determined. The sharp rectangular area of removed hair shown in Figure 10 indicates very well the sharpness of collimation of the neutron beam. During the past two years a considerable number of cancer patients have been treated with neutrons with encouraging results, and I want to show one case primarily as a matter of historical interest, for it is one of the earliest cases. This patient had a carcinoma involving extensively the jaw bone, and he had received no other treatment prior to the neutron therapy - as contrasted to most of the early cases which had histories of prior treatment with X-rays or radium. He was treated over a period of about a month, and Figure 11 shows the effects of the treatment some weeks later. One observes that the skin has shown a very pronounced reaction, and there is a suggestion that the tumor itself is beginning to shrivel up. At least, at this stage we recognize that the neutrons have done something! The next figure shows the patient several months later. The skin has healed, and the tumor has evidently disappeared, being replaced with scar tissue. Now nearly a year later, there is no evidence of the tumor, and the patient appears in good health. I know that Dr. Stone, Dr. Larkin and my brother would not want me to give

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the impression that this case is typical and that neutrons are producing miraculous results. Similar results have occasionally been obtained with X-rays and radium, and my medical colleagues are not ready as yet to come to any conclusions as to the relative value of neutrons and X-rays in clinical therapy; but it is proper for me to say that they are very much encouraged and they think that there is every likelihood that after some years of work they will find definitely that for some tumors, at least, neutron therapy will be most effective. In my judgment neutron therapy will eventually take an important place along with surgery, X-ray and radium in the treatment of cancer. Synthetic Radioactive Tracer Atoms One of the early results of atomic bombardment was the discovery that neutrons could be knocked in or knocked out of the nucleus to produce synthetic radioactive isotopes of the ordinary elements. Thus, for example, the nucleus of the ordinary sodium atom contains I I neutrons and 12 protons, 23 particles in all, and so it is called sodium 2,3 (Na 2 3 ); and by bombardment it was found that a neutron could either be added to make sodium 24 or subtracted to make sodium 22, both isotopic forms not occurring in the natural state. The reason that these synthetic forms are not found in nature is that they are energetically unstable. They are radioactive and in the course of time blow up with explosive violence. Sodium 24 has a half-life of 14.5 hours, i.e., it has an even chance of disintegrating in that time, C 72 3

turning into magnesium by the emission of an electron. Sodium 11, on the other hand, has a half-life of 3 years and emits positive electrons, transforming into stable neon 11. These artificial radioactive isotopes of the elements are indistinguishable from their ordinary stable relatives until the instant they manifest their radioactivity. This fact deserves emphasis, and it may be illustrated further by the case of chlorine. Chlorine consists of a mixture of two isotopes, 76 per cent of CI 35 and 24 per cent of CI 37 , resulting in a chemical atomic weight of 35.46, which is the average weight of the mixture. B y elaborate technique, to be sure, it is possible to take advantage of the extremely slight difference in chemical properties and bring about separation of these isotopes, but in ordinary chemical, physical and biological processes, the chlorine isotopes are indistinguishable and inseparable. There are artificial radioactive isotopes CI34 and CI 38 , and these likewise are indistinguishable. In fact, CP 4 is more nearly identical in properties to the natural isotope CI 35 than is the other natural isotope CI 37 , And again I would say that the radioactive characteristic of CI34 becomes evident only at the moment it blows up to turn into the neighbor-element sulfur. In these radioactive transformations of the artificial radioactive isotopes, the radiations given off are so energetic that radiations from individual atoms can be detected with rugged and reliable instruments called Geiger counters. Thus, radioactive isotopes can be admixed with ordinary chemicals to serve as tracer elements in complicated chemical or biological processes. C 73 3

I should like to cite several recent researches illustrating the power of this radioactive labelling technique. Radioactive Iodine and the Thyroid Gland As is well known, the thyroid gland takes up iodine in very large quantities, and the abnormalities in function of the thyroid are responsible for many human disorders. Doctors Joseph Hamilton and Mayo Soley have been studying the thyroid function for some time now, using radioactive iodine as an indicator. The general procedure is to include radioactive iodine in the food of animals or human beings and to follow the course of the iodine by measuring the radioactivity of dissected parts of the animals or of samples of the body, particularly next to the thyroid (Figure 12). In this way extensive studies of the uptake of iodine by the thyroid in health and in disease have been made and typical results are shown in Figure 13. Normally the thyroid takes up 3 or 4 per cent of the iodine taken in the food in the course or one or two days. That to my layman's mind is a surprisingly large uptake, considering how small a part of the body the thyroid gland is. In various abnormal conditions, particularly hyperthyroidism, the uptake reaches the surprising value of 30 per cent, and I believe Dr. Hamilton has observed patients in which the uptake has been as great as 70 per cent. It is quite outside of my province to discuss what these observations mean, but I am sure you will agree that they do illustrate the power of the tracer technique in finding out what is going on in various physiological processes. C 7 0

Biological Identification of Element 85 I should like to relate here a most interesting story now more than a year old in connection with these thyroid studies. Doctors Dale Corson, Kenneth MacKenzie and Emilio Segre at Berkeley had some evidence of the production of element 85 by the bombardment of bismuth with 32, million volt alpha-particles from the cyclotron. As element 85 had heretofore not been discovered, its chemical properties were not known, but from its place in the periodic table it was a reasonable likelihood that it would prove to be a halogen similar to iodine; in fact, it had been given the name eka-iodine. I t occurred to Dr. Hamilton that, if the new radioactive material which Doctors Corson and MacKenzie and Segre had obtained was eka-iodine, it might be selectively taken up by the thyroid like ordinary iodine. On this hunch, they gave the unknown new radioactive substance to a patient having a nontoxic goiter, one of the kind that takes up a great deal of iodine. They measured the radioactivity of the thyroid several days later, and amazingly enough about 10 per cent of the radioactive material was found in the thyroid gland. I suppose Dr. Hamilton drew the conclusion that it was interesting that element 85 is taken up by the thyroid much as is iodine, but the physicists regarded the experiment as a clinching biological proof or identification of element 85! In the meanwhile, the chemical properties of this element have been worked out in our laboratory, and one more gap in the periodic table has definitely been closed.

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Calcium and Strontium Metabolism I should like now to describe briefly some very interesting unpublished work of Dr. David Greenberg, who has been studying calcium and strontium metabolism in animals. I t had been shown earlier by Dr. Charles Pecher that the metabolism of these two elements is surprisingly similar. Dr. Pecher fed rats a diet containing strontium rather than calcium with the result that strontium phosphate was laid down in the bones in place of calcium phosphate. I understand that in this way some of his animals had bones containing almost half and half strontium and calcium, and yet the animals seemed to get along very nicely. In his studies of bone metabolism Dr. Greenberg has been using more radioactive strontium than radioactive calcium because the former is available in larger amounts, as it is at the present time being produced in the medical cyclotron in Berkeley in large quantities for therapeutic purposes. One problem upon which he has shed interesting light is the role of vitamin D in the cure of rickets. He fed a group of rats having rickets food containing radioactive strontium, and a similar group of animals was given in addition vitamin D. Then he followed over the course of time the excretion and retention of the strontium by observing the radioactivity of the excreta and tissues of all the animals. The results are shown in Figure 14, where it is seen that the vitamin D animals excreted less strontium in the feces while more appeared in the urine. These observations show that one function of vitamin D is to promote the absorption and retention

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of the strontium (and presumably calcium) from the intestinal tract. Next Dr. Greenberg injected suitable solutions of radioactive strontium into the blood stream of two groups of rachitic animals - one group being fed vitamin D. Again the radioactivity of the excreta was observed, and it was found that the feces showed slightly more activity while the urine considerably less for the vitamin-D-fed animals. These observations indicated that, beside promoting absorption of the strontium from the intestine into the blood stream, vitamin D also promotes some kind of a process of mineralization of bone, and this, I am told, is a fundamental point in the matter. Dr. Greenberg has been studying hyperthyroidism also. One of the manifestations of hyperthyroidism is that the bones get soft, calcium evidently being drained from the bones, resulting ultimately in such weakening that fractures occur. Again he fed radioactive strontium to two groups of animals, one group in the hyperthyroid condition, and the other normal controls, and observed the radioactivity of the excreta with the results shown in Figure 15. In the feces of the two groups the differences were not very great, but in the urine the hyperthyroid animals excreted about twice as much as the controls, indicating that in the hyperthyroid condition the excretion from the blood stream is much greater. Thus, the abnormality in the hyperthyroid animals is not a question of absorption but rather is one of excretion. Next the animals were injected with radioactive strontium so that the question of absorption was not involved, and, as expected, it was observed again that

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the hyperthyroid animals excreted in the urine about twice as much as the controls. The conclusion to be reached from these observations, according to Dr. Greenberg, is that the decalcification of the bone in the hyperthyroid condition has to do with the greater metabolic activity involving the greater rate of excretion of material which drains away the calcium from the blood stream and thereby from the bone. Radio-Autography Another way of using the tracer elements in biological work is literally more picturesque and in some respects is a much simpler technique. It is called the method of radio-autography and is illustrated in Figure 16. Here some radioactive zinc was placed in the nutrient solution of a tomato plant, and the uptake of the zinc in the tomato fruit was observed by slicing the fruit and placing the slides against a photographic plate. The radioactivity produced a picture of the distribution of the accumulated labelled zinc throughout the fruit. My colleagues in plant nutrition in Berkeley, Professor J. R. Hoagland, Dr. Perry Stout and others, have been studying the distribution of zinc in tomatoes in this way, following this phenomenon all of the way from the earliest stages of formation of the fruit to maturity as shown in the figure. The extent of my knowledge of this subject is indicated by the fact that it was complete news to me that zinc is an essential element in tomatoes! It is present in only a few parts in a million.

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Another interesting radio-autograph is shown in Figure 17, which is a section of a cancerous thyroid gland taken from a patient who had been given radioactive iodine the day before. The microscopic section was placed against a photographic plate, and the developed image showed where the radioactive iodine was deposited in the thyroid tissue. The magnification of the image is so great that the individual photographic grains can be seen, and there is enough detail to make it evident that the iodine is not deposited in the cancerous tissue but is found only in the normal thyroid material. I shall not attempt to discuss the interesting information along this line that my colleagues Doctors J . G. Hamilton and M. H. Soley have obtained in this way. Another interesting example is that of Dr. R . Craig, who has been studying the physiology and metabolism of insects. I think you will agree that a detailed study of the physiology and metabolism of insects would probably be a very difficult technique, but Dr. Craig has been able to get much useful information along this line very easily by radio-autographs. An example of the distribution of labelled phosphorus in a moth larva is shown in Figure 18. Radio-autographs of the distribution of labelled phosphorus and strontium are shown in Figures 19 and 20. Here we see that both of these elements are deposited largely in the skeletal structure, the phosphorus being more generally distributed in the bone marrow and soft tissues while the strontium was deposited more selectively in the bone structure. C 79 3

Radiophosphorus Leukemia is a disease of the white blood cells wherein the white cells multiply excessively, ultimately crowding out the red cells and producing an anemia, and so on to a fatal result. One treatment of the disease is to irradiate the whole body or certain parts of the body, such as the spleen, with X-rays. Such treatments frequently cause the white count to decrease practically to normal and temporarily produce a very beneficial result, but the X-ray treatment is only of temporary benefit, for ultimately the disease reaches a stage wherein it is not affected by such therapy. It occurred to my brother, Dr. John Lawrence, that, since phosphorus is deposited in the bones and bone marrow, where the white blood cells are formed, radioactive phosphorus might be especially effective for the treatment of leukemia. If whole body irradiation with X-rays produced a beneficial result, it might be that much better results would be obtained by the localized ionization produced by the radioactivity of the phosphorus at the site of the disease in the bone marrow. Accordingly, Dr. Lawrence looked into the matter, first of all by carrying out some experiments with mice having the disease. He fed animals radioactive phosphorus and observed the excretion and distribution of the phosphorus over the animals, finding among other things, that leukemic cells have an extraordinarily great appetite for phosphorus, for those tissues in which the leukemic cells had infiltrated were found to be much more radioactive than other tissues. These interesting 8

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observations with the animals gave all the more reason for hopefulness that the radioactive phosphorus would be useful clinically in leukemia. Dr. Lawrence has in the past two years treated a considerable number of leukemia patients with radioactive phosphorus and has obtained very interesting results. A typical case is shown in Figure 2 1 , where it is seen that a patient who had a white blood count of some 200,000 was given successive small doses of radioactive phosphorus over a period of several months, bringing the white count down to normal, around 10,000, after which the disease could no longer be diagnosed in the patient. This example is by no means an exception but is rather typical of the results obtained with the radioactive phosphorus. Since the treatments have been carried on hardly more than two years, it is too early to evaluate the ultimate usefulness of this new therapy. However, I am sure my brother would agree with the statement that radioactive phosphorus therapy gives the patient many more comfortable days of life than other methods of treatment, but it is too early to say whether complete cures will be effected. Radioactive Strontium and Osteogenic Tumors The fact that strontium is deposited in the hard structure of the bone suggested to Dr. Pecher that osteogenic tumors might have a great avidity for radioactive strontium, in which event the material might be effective in the treatment of this class of malignancies. For about a year now in our laboratory several patients

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having generalized bone metastases have been given radiostrontium with encouraging results - relief of pain and general improvement of clinical condition. It is not appropriate here to go into this subject extensively, but I should like to describe some very recent observations he has made on the deposition of radioactive strontium in an osteogenic carcoma. Several months ago a young boy with an advanced case of osteogenic sarcoma in his leg came to the clinic, and he was fed some radioactive strontium in his food several days before it was planned to amputate his leg. The amputated leg was X-rayed and also sectioned and placed against a photographic plate in order to get a radioautograph of the strontium distribution, and the results are shown in Figure 11. Here it is seen that there is a surprisingly large uptake of the strontium in the osteogenic tumor. In another patient who had an osteogenic sarcoma is seen the isolated nodule of sarcoma, which was extremely radioactive following the administration of radio-strontium. The radioactivity of various tissues was measured, and it was found that the uptake of the strontium in the bone was of the order of magnitude of a hundred times that of the soft tissue, and in the osteogenic sarcoma the uptake was roughly five times greater than that of the bone. Thus was observed an extraordinarily selective deposition of the radioactivity in the tumor, indicating that we may have here a very good means of treating this disease. I am told that the treatment of these bone tumors with strontium is going foward clinically with encouraging results, but again it is too early to draw any broad conclusions.

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Radioactive Carbon and Photosynthesis The mechanism of the process whereby green plants utilize solar energy to photosynthesize organic compounds from carbon dioxide and water is little understood although it has been the subject of study by scores of eminent scientists for centuries. In this process the solar energy is stored as carbohydrate, protein, etc., and this chemical fuel is the source of energy for the nonphotosynthetic systems. In fact, the ability to reduce carbon dioxide and use it as the only source for the synthesis of carbon compounds has provided a basis for the classification of all living systems into "autotrophes" systems capable of existing entirely on carbon dioxide and "heterotrophes" - systems requiring more elaborate foods. A fundamental difficulty in studying the plant photosynthesis is the inability of the chemist to distinguish the carbon entering the system in the primary process from the carbon already present. The use of a radioactive labelled carbon obviates this difficulty and renders it possible to trace the various chemical reactions in which carbon dioxide enters in photosynthesis. M y colleagues, Dr. S. Ruben and Dr. Martin Kamen (who have educated me on this subject), have made a very significant start in this direction, using a rather shortlived radioactive isotope of carbon, C 1 1 (half-life 21 minutes). While the work is still very much in its infancy, it already appears that the guesses made with regard to the mechanism of photosynthesis in the past are far from correct. Thus, it has been supposed that

likely intermediates in the reactions whereby carbon dioxide finally is synthesized into carbon chains are formaldehyde, simple organic acids, such as oxalic acid, citric acid, etc. However, none of the simple low molecular weight compounds have been found to contain any labelled carbon. In fact, the first substance detected with activity is at least ten times heavier than the intermediates mentioned. By means of the labelling technique, it has been possible to observe that carbon dioxide can be incorporated reversibly in an exchange reaction with a compound present in the cell in the absence of light, and the evidence indicates this compound to be of high molecular weight and to contain carbon, hydrogen and oxygen groupings typical of organic acids. These observations fit in well with others made by investigations other than the labelling technique, and it is not too much to hope that progress in understanding the essential mechanism of photosynthesis will be more rapid than it has been. With regard to the heterotrophes, one ordinarily does not consider that carbon dioxide fulfills the role of a metabolite in such systems. Nevertheless, when a typical heterotrophic system, such as yeast, is allowed to carry on fermentation in the presence of labelled carbon dioxide, much active carbon is found fixed or reduced and incorporated in cellular organic compounds. A very simple case may be cited. There exist species of bacteria which ferment alcohol, producing methane, water and carbon dioxide. Thus. 4CH3OH -» C0 2 + 3CH4 + a H 2 0 Cg4 3

In this process, it has been suggested that methane may originate not from the alcohol but from carbon dioxide despite the fact that carbon dioxide is produced. This point has been investigated using labelled carbon, and indeed it has been found that a large fraction, if not all, of the methane produced originates from the carbon dioxide and not the alcohol. In still another species of bacteria which produce carbon dioxide, ammonia and acetic acid from anaerobic fermentation of uric acid, the synthesis from carbon dioxide of acetic acid, CH 3 COOH with both carbons labelled has been observed. Here a two-carbon compound has been made from carbon dioxide by a system ordinarily supposed incapable of synthesizing a carbon chain from carbon dioxide. Many more such systems have been studied, and it now appears that carbon dioxide may be used specifically as a source of carbon in the synthesis of the organic compounds by both autotrophes and heterotrophes. Such a conclusion could not have been reached with many of these systems because the entry of the carbon dioxide was masked by the excretion of carbon dioxide from the oxidation of the organic substances supplying the energy for the metabolic process. It must be emphasized that the pickup of labelled carbon dioxide in these systems may be due entirely to simple exchange processes, but the evidence from other types of experiments has been held to indicate that carbon dioxide plays the role of a specific metabolite, and much that is obscure in present knowledge of fermentation processes is clarified if the concept of utilization of carbon dioxide by heterotrophes is employed. Cg5 3

T h e Giant Cyclotron These examples of applications of recent discoveries in the field of nuclear physics to biological problems, I trust, will convey not only an appreciation of the usefulness of these new techniques in solving problems of the life sciences but also will indicate something of the richness of the phenomena in the nucleus brought to light by bombarding atoms with atomic projectiles of millions of electron-volts of energy. As the energy of the bombarding particles has been increased by progressively improving the cyclotron, the range of the observed nuclear phenomena has even more rapidly increased, urging us on to higher energies. I should like to close this discussion with a couple of pictures (Figures 23 and 24) of the giant cyclotron now under construction, thanks to a generous grant from the Rockefeller Foundation, with which it is hoped to produce atomic projectiles of energies of a hundred million electron-volts or more. I am sure that this great machine will open new vistas, that it will bring exciting new pioneer days of discovery. What these will be only the future can tell!

C

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3

Commentaries L E S L I E A. C H A M B E R S

I

N a presidential address several years ago, one of our outstanding physical chemists discussed the factors which contribute toward the making of a great scientist. Among them he included the ability to present new data clearly and convincingly. To illustrate the point, he said, "For example, when I listen to a lecture by Irving Langmuir, it is necessary to keep saying over and over to myself, 'He's wrong! I know he's wrong,' or I find myself believing what he says whether it is wrong or right." While I have never found it necessary to defend myself against the teachings of Dr. Langmuir, I do share with Professor Bancroft the implied recognition of the beautiful clarity with which our speaker makes some of the most complex phenomena that have come within the broad range of his analytical mind appear simple, logical, understandable, and usable. Perhaps no other phase of Dr. Langmuir's research effort has impinged so directly and challengingly on biological research, as has that summarized in the address he has just presented. At least the implications of these studies of protein films are more immediately apparent to a biologist. C 87 3

The physiologist can measure the environmental requirements of complete living cells, and he can measure the chemical, thermal and electrical by-products which result from maintenance of the steady state, or from activity of the entire unit. The biological chemist has been able to determine the empirical composition of cells and to show that the various elements are combined, at one organization level, into certain definite building units, notable among them being the proteins. It is the wide gap between the relatively simple protein building blocks and the exceedingly complex structural and functional organizations represented by the entire cell that is so baffling. Living organisms are not simple aqueous solutions of proteins, fats, carbohydrates and salts bound by inert retaining barriers. On the contrary, these molecules interlace into membranes, micellae, megamolecules, coacervates, mitochondria, nuclei, chromosomes, sols, and gels, all exhibiting properties not now predictable from the sum of the known properties of the building blocks, all constantly being decomposed and replenished, yet all maintaining a strict constancy of architecture and function, apparently as a result of their organization in turn into steady state systems requiring only a suitable source of energy and an adequate sink for maintenance. The methods of handling and analyzing protein monofilms developed by Dr. Langmuir and his associates present to the biologist a powerful tool for the study of the types of protein aggregates which may occur in living objects. We have seen how certain investigators are applying the procedures, and we have heard at least

n88 3

one new theory today which should stimulate a flood of new investigations of the old, old problem of cell permeability. The extreme usefulness of these new research tools can best be emphasized by calling attention to still more of the interesting results obtained through their employment. In our own laboratory we have undertaken a study of the mechanical properties of films of highly purified proteins and the variation of these properties with the ionic composition of the substrates on which the films are formed. It has been found possible to characterize the individual proteins in terms of compressibility or elasticity as rather easily defined functions of substrate pYi and of the relative degree of protein expansion permitted prior to the initial compression. Upon extrapolation to the hypothetical condition of infinite expansion relative to the final compressed state, all of the globular proteins appear to exhibit the same compressibility. Furthermore, this limiting compressibility is the same regardless of the ionic concentration of the substrate. In this hypothetical extrapolated state the ionic factors influencing the elastic properties of the membrane are practically non-existent. Hence it seems that the compressibility constant so obtained must indicate a fundamental constancy in the architecture of the backbone structure in the fabric. The interlocking, coherent framework of the film must be nearly the same whether the material originally spread be albumin, insulin, globulin, or pepsin. Certain of the alcohol soluble proteins, on the other hand, yield films of an entirely different structural charC89 3

acter. If our tentative interpretation is correct, this analytical isolation of the factors influencing compressibility should assist in analysis of the inter-unit forces operative in these gabricoid aggregates of proteins. After establishing some of the compressibility data for films of pure proteins we have proceeded to a similar analysis of films formed from known mixtures of two or more of the substances, or mixtures of pure proteins with phospholipids. While these studies are in a very preliminary form, it can be said that such mixed films show reproducible mechanical properties of such character that they are derivable theoretically from the interaction of the previously determined properties of the individual components. Possibly, in this step-wise fashion, we may some day be able to study films equalling in complexity of composition those known to occur in living cells. As another illustration of the use of Dr. Langmuir's film techniques, we may cite what has been accomplished in the study of the antigen-antibody reaction. Using deposited monofilms of antigen in contact with homologous antibody solutions of known concentration, and employing a modification of the Blodgett-Langmuir technique for determining increments in thickness, we have been able to follow the course of the reaction in time and to demonstrate that the combination, under such conditions, obeys a bimolecular reaction law. These observations are chiefly notable for what they indicate to be possible. One need only recall the numerous research applicaC 9« 3

tions of the film technique mentioned by Dr. Langmuir, and to exercise the imagination lightly, to see that this attack on fundamental problems of biology offers enormous promise. In recent years powerful, and sometimes ponderous, tools have been placed in our hands, the full potentialities of which are just being realized. The ultracentrifuge, the electrophoresis cell, the electron microscope, the cyclotron, the X-ray diffraction camera and other instruments of the sort have made of biology a field full of new horizons. With thanks to Dr. Langmuir, his associates, and disciples, we can now include in this formidable array of weapons the interface between air and water. J . R. D U N N I N G

P

ROFESSOR LAWRENCE has already given such a splendid picture of the high spots of the cyclotron and its applications to various fields that it is very difficult to add anything to it. However, one should certainly say that without the cyclotron, which Professor Lawrence and his collaborators have pushed to such a high peak in looking forward to even a higher peak in the future, most of these applications would have been quite impossible, for the cyclotron really makes whatever artificially irradiated isotopes and neutrons there are available in significant quantities for application to other fields. Certainly, the future will reveal the possibilities of applying artificially radioactive isotopes as tracers in the fields of physics and chemistry and over into the C91 3

fields of biology and physiology and into the fields of medical therapy. At the same time there are many applications in the field of industry. They are just beginning to open up. I am sure it is safe to say that the field is just really beginning. As the future expands, we will see many applications that we have scarcely dreamed of today. One should perhaps call attention, along with the interesting possibilities of the future, to some of the limitations of the radioactive isotopes so that we won't go too far. One is that radioactive isotopes are essentially identical, in their form and in their chemical behavior, to ordinary isotopes of the same elements. All of the 91 elements can now be made radioactive. All of them can be, therefore, labeled, followed and traced through physical and chemical and biological processes. There is just one little reservation that one must make, and that is, that the light elements, such as carbon 13, have small effect, but for H 3 , which is one of the interesting isotopes and has many applications, there is just enough difference in mass between H 3 and H 1 , the factor of 3, to show up a little bit in the rate of chemical reaction and in various chemical processes. So one has to be just a little bit careful in extrapolating as to what happens to ordinary hydrogen by using, as an example, H 3 as a tracer, but that is a small difference to be accounted for. The correction is quite negligible and ordinary and radioactive isotopes are completely identical for all practical purposes. There is just one other caution that should be mentioned, and that is, in the case of biologiC 9" 3

cal experiments it has been fairly well demonstrated that one must be a little bit careful about introducing radioactivity into the animal organism. Biological processes are affected to some extent if large amounts of radio-activity are present. Dr. Kenney and his collaborators at the Memorial Hospital showed that the phosphorus metabolism, general phosphorus content and intake of animals and human beings are affected appreciably by the amount of phosphorus, of radio-active phosphorus, that is fed; in other words, the irradiation does affect physical-chemical processes. That simply means that one must be careful to use very sensitive methods, which fortunately are available for study of radioactive distribution of materials in plant and animal processes. Fortunately, the count is so sensitive that it takes single radio-active atoms. There is no need to use some of the cruder instruments, because of the extreme sensitivity of what is already available. It seems that there is certainly no difficulty at all if one uses small quantities and highly sensitive instruments. There is just one other point I would like to comment upon, and Professor Lawrence has already emphasized it; that is, it seems, while one must be very cautious in saying too much about the possibilities of radio-active isotopes and of neutron therapy, there are really possibilities in this field which have not been possible with X-rays. In X-rays you must expose either the whole animal, as in the case of leukemia, or, in the case of a local treatment of a cancerous condition, you must use C93I1

X-rays which spray the whole area; they ordinarily always produce maximum damage on the surface, so that the skin damage limits the amount of irradiation which can be used. In the case of the neutrons and in the case of the radioactive isotopes, we at last have the beginnings of something which can selectively attack the cancerous condition and not the surrounding tissue. There is the possibility of localizing selectively the radioactive materials in the treatment of cancerous tissues, as has been mentioned by Professor Lawrence, and there are certainly many new possibilities to study there. It is also possible to localize neutron damage through implanting in the cancerous tissue materials such as boron and lithium, which are selectively disintegrated by neutrons when the cancerous regions are exposed to the neutrons from the cyclotron. There is a great deal of work to be done in the future, and it does seem that here at last we have possibilities for selective processes that were not present with X-rays. How much is possible to prove remains to be seen. Fortunately the production of neutrons and production of radioactive isotopes have been going up at an ever-increasing rate. I don't know how one can extrapolate the curve of radioactive isotopes over a period of ten years; in fact, ten years ago it was almost zero. So one can say that there has been an almost infinite increase in the amount of isotopes available. However, each year sees a factor of 10 to 100 in the number available, rather in the amount of the various isotopes available. What the new cyclotron will bring, as Professor Lawrence has said, it C 94 3

hard to say. What the other various processes that are contemplated for the liberation of atomic energy will bring and how much will be possible toward general therapy in the future, no one can say. Certainly, the future is an interesting thing to contemplate.

n 95 3

F I G U R E I . A view of the 225-ton medical cyclotron at the Crocker Radiation Laboratory. F I G U R E 1. The 16 million electron-volt deuteron beam emerging from the cyclotron chamber into the air. An indication of its size may be gained from noting the jneter stick placed below the beam.

F I G U R E 3 . The cyclotron as it now appears surrounded by water tanks that furnish a 5-foot barrier to protect the laboratory personnel from the dangerous radiations from the cyclotron.

FIGURE 4. Ionization produced in a Wilson cloud chamber filled with a mixture of air, hydrogen and water vapor after bombardment with neutron rays and gamma-rays from the cyclotron. The thin tracks of ions were produced by secondary electrons liberated by the gammarays, while the thick and very dense tracks were produced by the recoil protons resulting from collisions of neutrons with the hydrogen atomic nuclei. This picture demonstrates the more localized and intense ionization produced in tissues by neutrons when compared with X-rays or gamma-rays.

FIGURE 5. Chromosome fragments produced after treatment of a mouse sarcoma 180 with X-rays.

DOSE IN ROENTGENS

FIGURE 6. Per cent normal anaphase chromosomes in the bean Vicia faba as a junction of dose in roentgens at various times after treatment with X-rays.

DOSE IN "N" UNITS

FIGURE 7. Per cent normal anaphase chromosomes in the bean Vieta faba as a function of dose at various times after treatment with neutrons.

NEUTRON

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F I G U R E 8 . The nuclear reaction which is graphically represented here indicates the mode in which the bombardment of beryllium atoms by deuterons results in the release of energetic neutrons.

F I G U R E 9 . The treatment port from which the collimated neutron beam emerges is shown in this picture. It can be seen that the patient is placed against the port in a manner similar to the technique employed for deep X-ray therapy.

F I G U R E I O . The denuded area on the back of the rabbit was produced by the action of the neutron rays. The sharp delineation of the hairless area indicates the efficiency of collimation of the neutron beam.

F I G U R E I I . The marked skin reaction on the side of this patient's face indicates the action of the neutron ray. Here again it is very evident that the neutron beam is sharply collimated. The small circular depression to the left of the patient's mouth is the region where the tumor had broken through the skin and now has apparently begun to regress.

F I G U R E I I . The technique employed for the measurement of the uptake of radio-iodine by the thyroid gland in situ. The counter tube was placed against the thyroid gland to determine the gamma-radiation from the accumulated radio-iodine.

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ACTIVITY 48 HOURS AFTER ADMINISTRATION F I G U R E 1 4 . A chart indicating the action of vitamin D upon the strontium metabolism of rachitic rats. Vitamin D-treated and untreated rats with rickets received radiostrontium by mouth and intravenously. The excreta was collected over a 48-hour period and its content of labelled strontium determined by measuring the radioactivity of the urine and feces from the different groups of animals. At the end of the 48-hour period the animals were sacrificed and the retention of labelled strontium determined in the bone and in the body as a whole. It will be noted that the vitamin D-treated animals excreted considerably less radiostrontium in the urine when it was injected. When the labelled strontium was administered by mouth considerably less strontium was found in the feces, suggesting that vitamin D aided in the absorption of the radiostrontium. The retention of the labelled strontium was significantly elevated in both the bone and the total body in the vitamin D-treated animals.

ACTIVITY 163 HOURS AFTER ADMINISTRATION F I G U R E 1 5 . The action of the thyroid hormone upon the mineral metabolism of bone. The increased elimination of radiostrontium is noted in hyperthyroid animals. The animals which received radiostrontium by injection indicated that the hyperthyroid group retain less than the normals. The reverse was noted when the radiostrontium was administered by mouth.

F I G U R E 17. Photomicrograph of a section and its corresponding radio-autograph from, a patient with a cancer of the thyroid (X 60). The diffuse cellular area covering the right half of the section is made up of cancerous thyroid tissue. To the left are three small islands of uninvaded thyroid tissue which accumulated most of the radio-iodine.

F I G U R E 1 6 . The uptake of labelled zinc in the fruit of the tomato plant is demonstrated by the technique of radio-autography. The light areas indicate the regions of maximum deposition of the labelled zinc in slices of the tomato fruit. It can be seen that the seeds apparently accumulate most of the absorbed radiozinc.

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w «M FIGURE 19. A comparison

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F I G U R E 2 1 . The chart indicates the response of the blood count of a leukemic patient to the administration of radio-active phosphorus. The three small arrows at the base of the chart represent the time of therapeutic administration of this agent. The heavy dotted line indicates the white blood count which can be seen to fall sharply after the administration of the radiophosphorus.

F I G U R E 2 3 . Artist's conception from early plans of the giant cyclotron. The beam is seen extending to the left for a distance of 140 feet caused by the passage of hundred million volt atomic bullets created in the accelerator chamber.

F I G U R E 11 (opposite page). A radiostrontium radio-autograph and the corresponding radiograph of a thick section of an amputated leg from a patient with osteogenic sarcoma. The tumor, which is indicated by the arrow on the radiograph, has extended out into the surrounding soft tissue. The radio-autograph demonstrates that the radiostrontium was selectively deposited in the tumor with small amounts in the surrounding bone and that relatively little was accumulated in the soft tissues.

F I G U R E i\. A recent view from above of the giant cyclotron magnet now under construction on the University of California campus at Berkeley. All but the upper pole construction is completed. The whole involves J,700 tons of steel and will have 300 tons of copper in its windings. The auxiliary equipment, as seen in the artist's conceptions, is still to be constructed.