The Mechanistic Conception of Life (The John Harvard Library) 9780674559509, 0674559509

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THE JOHN HARVARD LIBRARY Bernard Bailyn Editor-in-Chief

THE JOHN HARVARD LIBRARY

THE MECHANISTIC CONCEPTION

OF LIFE By

JACQUES LOEB

Edited by Donald Fleming

THE BELKNAP PRESS OF HARVARD UNIVERSITY PRESS Cambridge, Massachusetts 1964

© Copyright 1964 by the President and Fellows of Harvard College All rights reserved Distributed in Great Britain by Oxford University Press, London Library of Congress Catalog Card Number 64-13426 Printed in the United States of America

CONTENTS

Introduction by Donald Fleming vii

A Note on the Text xii

Preface 3 THe MECHANISTIC CONCEPTION OF LIFE

1. The Mechanistic Conception of Life s) 2. The Significance of Tropisms for Psychology 35

System 64 Vision TO

3. Some Fundamental Facts and Conceptions concerning the Comparative Physiology of the Central Nervous

4. Pattern Adaptation of Fishes and the Mechanism of

phology 78

3. On Some Facts and Principles of Physiological Mor-

6. On the Nature of the Process of Fertilization 105 7. On the Nature of Formative Stimulation (Artificial

Parthenogenesis ) 116

Act of Fertilization 143

8. The Prevention of the Death of the Egg through the

9. The Role of Salts in the Preservation of Life 154

on Animals 178 Index 211

10. Experimental Study of the Influence of Environment

INTRODUCTION

Few significant books of the twentieth century cry out for historical placing as much as Jacques Loeb’s Mechanistic Conception of Life of 1912. We instinctively feel that book and author alike belong to the past out of all proportion to the time that has actually elapsed. A scientist can reveal himself in three ways: through his empirical findings; through his basic animus in research; and through his life-style in science, the role he tries to play in his professional capacity. We now expect him to publish his results but keep his animus to himself; and we expect his life-style to be intellectually contracted. We are prepared, indeed, to find him treading the corridors of power; and are not surprised to hear him pronouncing upon public issues generated by scientific developments—appeasing his conscience over the Bomb or slaking his thirst for power. What we do not anticipate is that he will project an integrated Weltanschauung tied to his own research. We do not concede to him what we despair of for ourselves, the power to bring the whole range of human perplexities under control. We may perhaps be willing to indulge him in a half-hearted effort to ‘“‘philosophize”’ over his researches from old age; but we regard

it as an embarrassing coda to his real work. By these lights, Jacques Loeb was shameless even in his prime. He brazenly paraded his mechanistic animus in the very title of his most famous book, organized his empirical findings about it, and pronounced ex cathedra on the most fundamental issues in morality and politics. He essayed a lifestyle in science that would blend the roles of philosopher,

vii

Vill INTRODUCTION moralist, reformer, and investigator. The question becomes how Loeb came by this omniscient life-style, this prodigally expansive conception of the scientist’s role and scope. He did not invent it. He was born in Germany in the middle of the nineteenth century and imbibed it from that time and place. It was a time and place when the mechanistic animus was taking hold and in the process eliciting antithetical life-styles in science.

One group of German mechanists at mid-century were a band of young experimental physiologists who simply wanted to get on with their work but found themselves intimidated by vitalists who smugly declared it was all in vain—the most fundamental processes of life would always elude a mechanistic analysis. Stung by these taunts, and perhaps to screw up their own courage, a quadrumvirate of rising physiologists— Helmholtz, Ludwig, Du Bois-Reymond, and Briicke—swore a famous mutual oath in 1845 to account for all bodily processes in physicochemical terms. This was intended as a program for research rather than the enunciation of a Weltanschauung. The Mechanistic Quadrumvirate and their sympathizers did not attempt to banish nonmechanistic conceptions from other

spheres. Though most of them were not religious, they did not undertake to proscribe religion for others. By no accident,

this tradition produced in Du Bois-Reymond the man who inscribed “Ignorabimus” on his banner to signify things we shall never know, “‘world-riddles” that science could never resolve. Mechanism was coextensive with scientific knowledge

but not with the range of legitimate curiosity. It was a classic formulation of the contracted life-style in science—demanding enough room to do one’s own research while side-stepping any cosmic pretensions. The upsurge of experimental biology produced the opposite response from the medical materialists, led by Jacob Moleschott of Das Kreislauf des Lebens (The Circulation of Life, 1852), Ludwig Btichner of Kraft und Stoff (Force and Matter, 1855),

INTRODUCTION ix and Carl Vogt of Kéhlerglaube und Wissenschaft (Superstition and Science, 1855). These men are best remembered for their outrageous dicta that man is what he eats, genius is a question of phosphorus, and the brain secretes thought as the kidney secretes urine. The core of their doctrine was that force and matter are always conjoined, with no necessity for materialists to account for the conjunction. Though the medical materialists actually did research, they did not invoke mecha-

nism as a mere postulate for the conduct of further investigations but rather as a philosophy of the universe to be bolstered by citing appropriate experiments but in no way confined to eliciting or explaining them. Here the medical materialists displayed their characteristic determination to reduce all things to a common measure within a homogeneous scheme. The world riddles despaired of by Du Bois-Reymond could be solved

by the same means as the riddles daily unlocked by science. The medical materialists were philosophical monists, vindicating for mechanistic materialism an infallible omnicompetence to the entire occasion of the universe. By the same token, they delineated the most expansive life-style that a scientist could possibly aspire to.

The historical mission of the medical materialists required that they should pronounce upon the ultimate issues in politics and religion for their bearing upon the environment of science. They saw in the established order in Germany a diabolical and indissoluble alliance of church and state, orthodoxy and

reaction, to put down freedom of thought in science and frustrate the application of scientific discoveries to the general welfare. They became socialists and revolutionaries who by subversion of church and state hoped to liberate science from the trammels upon its freedom and the obstacles to its social utility. The ideal of social justice which they envisioned was tightly bound to their fascination with the emerging science of nutrition and its correlate in agricultural chemistry. They demanded a maximizing of foodstuffs and equitable distribution

x INTRODUCTION of nutriment to lay the material basis for social and political equality in the actual sinews of the poor. All institutions that impeded the flow of nutriment to the masses must yield to reform or revolution. It was not without significance that the leading spokesman for the alternative tradition of mechanism, Du Bois-Reymond, was a pillar of the Prussian state. The great scientist who oscillated between the contracted style and the omniscient was the leading pathologist of the nineteenth century, Rudolf Virchow, the author of a celebrated essay of 1858 entitled ““The Mechanistic Conception of Life.”* The young Virchow was a fellow student with the Mechanistic

Quadrumvirate and a full participant with them in the flight from vitalism. He also shared their tolerance of faith, though not in scientific matters and not for himself. Every man, said Virchow, has the license to ask “transcendental’’ questions about the ultimate purpose of things, but he then leaves the “public” arena of science and enters “‘the secret chambers of his conscience.” By his general attitude of permissiveness toward transcendental speculation and refusal to assert a dogmatic materialism encompassing the entire universe, Virchow sought to differentiate himself from the life-style of the medical

materialists. Yet he overlapped with them in his social and political attitudes, and more significant, in his persistent effort

to ground these upon a scientific basis. Though never an avowed socialist, he held in his professional capacity as a pathologist that many forms of epidemic disease, particularly typhus, tuberculosis, and mental disease. were a malady in

the state induced by gross inequities in the distribution of wealth and power. The young Virchow, like the medical materialists, was a revolutionary who supported the German revolution of 1848. In mature life, he became the only great scientist in history to play a major role in politics, as chief of the liberal opposition to Bismarck. His record as a democratic 1“ijber die mechanische Auffassung des Lebens,” Vier Reden tuber Leben und Kranksein (Berlin, 1862); trans. In Virchow, Disease, Life, and Man, Lelland J. Rather, trans. and ed. (Stanford, 1958).

INTRODUCTION xi statesman was marred by his support of the Kulturkampf (a

term of his own coinage) against the German Catholics. Despite this unhappy episode, Virchow had a deep commitment to democracy, which he repeatedly sought to anchor to his pioneering researches in cellular pathology. He found an emblem of democracy in the human body—a society of individual cells, profiting from the association but each retaining its basic character as an independent focus of vitality. If the young Virchow came very close to embracing the omniscient style, he became more circumspect with age, and his tolerance of faith had always been a stumbling block. In his later years, he often grappled with a former student of his own who brooked no reservations about anything, the great German apostle of Darwinism Ernst Haeckel. Haeckel from a conservative youth grew continually more dogmatic in his monism, more sweeping in his pronouncements on everything under-above-and-in the sun, and more fiery in his social-

ism. He scoffed at Du Bois-Reymond for his Ignorabimus, lashed at Virchow for claiming that evolution was a mere hypothesis, professed an unbounded assurance that science would solve the world riddles, and inspired the formal organization of a body of monists. He became the Great Omniscient of his time in Germany. Jacques Loeb was born of a Jewish family in the Rhine Prov-

ince of Prussia in 1859—at the end of the decade in which the medical materialists fired their principal broadsides, the year after Virchow published his essay on “The Mechanistic Conception of Life,” and the same year as Darwin proclaimed the gospel appointed to Haeckel.* Loeb always remained a child of that moment in history, to whom the mechanistic *The standard biographical account is W. J. V. Osterhout, “Jacques Loeb,” Journal of General Physiology, 8 (1928), ix-xcii—reprinted in National Academy of Sciences, Biographical Memoirs, XIII. See also: T. Brailsford Robertson, “The Life and Work of a Mechanistic Philosopher. Jacques Loeb,” Science Progress, 21 (1926), 114-129; Robert L. Duffus, “Jacques Loeb: Mechanist,” Century Magazine, 108

(1924), 374-383; Paul H. de Kruif, “Jacques Loeb, the Mechanist,” Harper's Monthly Magazine, 146 (1922-1923), 181-190.

xii INTRODUCTION animus and the omniscient life-style were native. The impact of his general environment was compounded by his personal history. His prosperous merchant father was an ardent Francophile and admirer of the Enlightenment and the French Revolution, who encouraged the boy to read the eighteenth-century classics of free thought.° The speculative virus took and Loeb’s original intention was to become a philosopher. On entering the University of Berlin for this purpose in 1880, he promptly concluded that the professors of philosophy were mere wordmongers. They neither could nor would make any real progress toward solving the problems they delighted in posing. When Loeb switched in disgust to biology, a casual observer might have supposed that he was liquidating his philosophical interests. In fact, however, the two phases of his student life were tightly bound in a single matrix. The question he turned upon the philosophers for not resolving was the same question he put to his biological

experiments: was there any such thing as freedom of the will? Loeb traced his lifelong obsession with this pre-eminently metaphysical issue to his youthful reading of Schopenhauer and von Hartmann, the philosophers of the will. Though Schopenhauer’s major work, Die Welt als Wille und Vorstellung (“The

World as Will and Idea”), was published as early as 1819, it was greatly expanded in 1844 and his real vogue commenced

with a volume of essays of 1851. This vogue was not yet exhausted in Loeb’s early manhood. Schopenhauer saw all organisms as the objectification of their own will to live: in the beginning was the will. The physical organism followed after,

and to this was annexed the intellect as merely one of the instruments the will decreed for its own use. In one sense, Schopenhauer was vindicating for the individual organism a tremendous freedom to enact itself at will, endowed with a perfectly harmonious complement of structures and attributes 3Qn Loeb’s father, see Robertson, ‘Loeb,’ 114-118; Duffus, “Loeb,” 375.

INTRODUCTION xill beyond any power of the environment to derange. Yet the much-vaunted freedom of the individual will was an illusion. For the rage to live upon which it turned was to Schopenhauer a malign imposition by the overriding Will of the universe, tirelessly demanding new victims for what he regarded as the torment of living. The despicable cunning of the whole scheme resided in making individuals believe that indulgence of their sexual drives was freedom rather than the operation of the

internal clockwork inserted by the cosmic Will to enslave them. Von Hartmann translated the Will of Schopenhauer into the Unconscious and effected a junction at second hand between Schopenhauer and Freud. Loeb never went into any detail about his indebtedness to Schopenhauer. They clearly shared not only an obsession with what Loeb called “the problem of will’ but a dogmatic conviction that freedom of the individual will was illusory. They also believed, fanatically, in ripping the veil from the illusion, stripping the pretensions from the overweening automatons who fancied themselves bestriding the world. Schopenhauer

and Loeb demanded access to the unmitigated Truth and commanded others to look upon it as steadily as themselves. Where they decisively diverged was over Schopenhauer’s pessimism. He was shocked and repelled by the reality from which he insisted on snatching the garment. Loeb reveled in the spectacle. To Schopenhauer it was obscene that men by their passional nature should be impotent to keep themselves from being churned into a frenzy of striving by the malignity of the cosmic Will disguising itself as individual spontaneity. In contrast, the young Loeb found a deep repose in the contemplation of determinism. He undoubtedly drew his satisfaction on this score from the depths of his own personality. But if he sought for confirmation of his native instinct from external sources, he could readily have found it in Virchow, some of whose writings he knew. Though we have no positive evidence, it is hard to believe that Loeb never read

Xiv INTRODUCTION Virchow on “The Mechanistic Conception of Life’ with its affirmation that to be in the grip of an ineluctable career devoted to a reasonable object was the greatest good accessible to man. One aspect of Loeb’s dissent from Schopenhauer’s gloom was his expectation of drastic social reform. He belonged to the class of determinists who perceive an inevitably enacted world of evils about them yet do not despair of shaping it toward some kind of millennium. Marx was another man of this stripe, and Loeb was a socialist. By no accident, they both had strong affinities with the medical materialists. Marx professed to despise and Loeb never mentioned them; but neither contempt nor silence is conclusive, for the medical materialists were among the least praised and least acknowledged shapers of nineteenth-century opinion. Marx did pay tribute to Ludwig Feuerbach, an open ally of the medical materialists. If Loeb did not know their writings or at least their ideas, it was the one serious gap in the raking fire of attention which he continually trained upon the intellectual life of his time. One thing is certain: he perceived in Bismarckian and Wilhelmine Germany the identical compacting of religious orthodoxy, militaristic nationalism, and political reaction into a monolithic whole which they had delineated in the previous generation. Like the medical materialists, he saw in the pursuit of military glory and national aggrandizement a calculated diversion of workingmen from their true interest in peace and the improvement of living conditions. He was also a Jew who saw German chauvinism and militarism as increasingly tinged with anti-Semitism and glorification of the master race. He never forgot his first acquaintance, about 1879,

with the writings of Treitschke, “the court historian of the King of Prussia,” on the superiority of the German “race.”° *The best expression of Loeb’s socialism is his article on the outbreak of the First World War: ‘Freedom of Will and War,” The New Review. A Critical Review of International Socialism, 2 (1914), 631-636. 5“Freedom of Will,” pp. 633-634.

INTRODUCTION XV Loeb wanted a remedy for this and all other forms of supersti-

tion; he wanted to improve the daily lot of the masses; and he wanted to vindicate his philosophy of determinism. Like the medical materialists before him, he concluded that science was the answer.

In this spirit Loeb went in 1880 to work with Goltz at Strasbourg on localization of function in the brain. He later described this as his intended “‘starting-point for an experimental analysis of the will.” What he can have had in mind is not clear, unless he conceived of brain surgery upon experimental animals as forcing their wills. In the event, he regarded the five years he spent with Goltz and the thesis he wrote on blindness induced by injury to the cerebral cortex as totally unprofitable for his purpose. The neurologists had failed him as the philosophers before them and he began to fear that he might be trapped in one impasse after another. In 1886 he moved on the University of Wiirzburg and suddenly his life snapped into focus. There he became assistant to the professor of physiology Adolf Fick and an intimate friend of the great plant physiologist Julius Sachs. Between them they initiated him into mechanistic physiology. No men were better equipped

to set him on this new path. Both put him in touch at one remove with the great Mechanistic Quadrumvirate of Helmholtz, Du Bois-Reymond, Ludwig, and Briicke. Fick was a student of Ludwig and Du Bois-Reymond, a slightly younger comrade in arms, and scarcely inferior even to them as a pioneer on the border between physics and biology. Sachs for his part took as his mission in life to make the same temper prevail among botanists. In his celebrated history of botany, he singled out for praise as one of the few creditable researches in plant physiology before his own the effort by Briicke of the Mechanistic Quadrumvirate to account in purely physical terms for the irritability of the “‘sensitive” plants. On the face of it, Fick and Sachs found in Loeb their most

receptive student, who gratefully accepted from them the gift of a new life. In another sense, he eluded them in the

Xvi INTRODUCTION very act of experiencing conversion at their hands. For him the revelation of mechanistic physiology did not come as an end in itself but as a new instrument with which to prosecute his metaphysical anxieties; a new limb to be grafted on to the

deterministic philosophy which he brought with him to Wiirzburg and never abandoned. Yet Fick in particular would have shuddered at the subordination of mechanistic science

to an all-encompassing metaphysical vision of the kind by which the mature Loeb signified his unbroken affinity with the medical materialists and other philosophical monists. Loeb had passed into the company of scientists like Fick for whom determinism was merely the definition of their line of work; but he was never truly of their number. For him it was a faith and a religion. The profound ambiguity in his relationship to the mechanistic physiologists did not keep Loeb from becoming the principal disciple of Sachs. Sachs had taken over from the Englishman

T. A. Knight (1806) and the Swiss Alphonse de Candolle (1832), and greatly amended, the concept of plant “tropisms” (from the Greek trope for turning)—obligatory movements elicited by physical stimuli such as light and gravity.° These were the theme of the research that Sachs was conducting to brilliant effect when he and Loeb were daily companions. To

Loeb they came as the answer to his private quest for the conceptual apparatus and experimental techniques to bring the behavior of animals under as rigid control from without as the growth of plants. He would found a science of animal tropisms.

The appeal of Sachsian tropisms to Loeb was bound up with his highly equivocal attitude toward Darwinism. He was delighted to see the havoc that Darwinism wrought among the religious and habitually cast his rather measured tributes

to Darwin in these terms, as another Galileo battling the

6The best account of research on tropisms down to Loeb’s own time is S. O. Mast, Light and the Behavior of Organisms (New York, 1911).

INTRODUCTION XVii obscurantists. Yet the satisfaction that Loeb could take in this

was tainted by the fact that evolution did not lend itself to experimental demonstration. He would settle for nothing less than the demonstrated power to transform one species into another at will. Anything else smacked of the hypothetical

and deductive. To the end of his life he made great fun in private of the conclusions drawn by palaeontologists from what he regarded as the insecure principle of the correlation of diagnostic fossils with the succession of geological strata.’ Of two animals abroad on the same day, he said, one might fall into a deeper hole than the other without being a more primitive species. Superficially joking remarks of this kind reveal Loeb’s enduring malaise on contemplating the historical dimension of scientific discourse. For him the only scientific “history” was that which could be compressed within the time scale of an actual observation of the unfolding phenomenon. Apart from his general skepticism about Darwinism, Loeb had specific occasion for alarm about its impact in the sphere of most immediate concern to himself as a disciple of Sachs proposing to revolutionize animal psychology. For Darwinism threatened to wipe out the line between men and animals in favor of the latter. Many German Darwinians, in particular, led by Emst Haeckel himself, engaged in an anthropomorphizing comparative psychology that was utterly antipathetic to the concept of animal tropisms. As man was no longer discon-

tinuous from the remainder of creation, they felt at liberty to confer human faculties upon the lower animals. Though they instinctively focused upon dogs and horses as if to show

that the repellent kinship with apes could be balanced by more congenial ties, Haeckel in the end carried the note to its ultimate conclusion by attributing souls not merely to plants and microorganisms but to crystals. He and Loeb were

at one in their socialism and their doctrinaire hostility to religion; but Loeb could never swallow Haeckel’s panpsychism. "De Kruif, “Loeb,” pp. 184-185.

a XVill INTRODUCTION

Where Loeb was trying to reduce the higher organisms to the level of Sachs’s tropistically driven plants, the “Darwinian”’

animal psychologists were working at diametrically cross purposes to elevate dogs and horses to the level of men, conceived as spiritual beings endowed with spontaneity. The menace of Darwinism had still another dimension for a disciple of Sachs. Darwin himself and his son Francis had addressed themselves in their book The Power of Movement

in Plants of 1880 to the very issues that lay at the heart of

Sachs’s concept of tropisms. And they pronounced upon these in exactly the opposite sense. They claimed to have discovered that all parts of plants were continually in random motion—

engaged in their terminology in “circumnutation.” Tropic stimuli were never primary but simply modulated onto a ground of spontaneous movements. Sachs never neglected an opportunity to disparage these experiments as “unskilfully made and improperly explained.’’® For his ardent sympathizer Loeb, they were even more unsettling. Darwin had unleashed a sentimental school of animal psychology while subverting at the source what Loeb regarded as the only bulwark against it, the Sachsian doctrine of tropisms. In the same winter of 1886-87 that Loeb experienced his initiation into mechanistic physiology at the hands of Fick and Sachs, the young Swede Svante Arrhenius was also working in Wurzburg at the height of his powers. Arrhenius dated from Wiirzburg his famous letter of 1887 to van’t Hoff announcing

his corollary to the latter’s theory of solutions. Arrhenius invoked electrolytic dissociation—ionization—of salts, acids, and alkalis in solution, as the explanation for the anomalies which remained in van't Hoff's otherwise extremely powerful conception of solutions as obeying the same laws as gases and susceptible of the same quantitative analysis. This tremendous advance in physical chemistry can hardly have been lost upon 8Quoted in Mast, Light, p. 21.

INTRODUCTION xix Fick. It ought not to have been lost upon Sachs, for the whole development was triggered by a long line of researches upon osmotic pressure in plants, as detailed by him in his history of botany. It is tempting to suppose that he and Fick joined in calling the attention of their protégé Loeb to the opportunities that were opening for investigation of the physiological role of ions and more generally for the assimilation of physiology to physical chemistry. It is more tempting still to suppose that Loeb and Arrhenius may actually have met in Wurzburg in this year of exploding horizons for each. The incontestable facts are that Loeb became an evangelist for physical chemistry as the key to biology; he was conducting experiments from the early 1890’s forward upon sea urchins immersed in salt solutions and subjected to alterations in osmotic pressure by changing the concentration; and his personal intimacy with

Arrhenius in the twentieth century is well authenticated. Whenever they first met, they had more in common than an interest in physical chemistry. They participated in the same unmistakable Weltanschauung of materialism in philosophy, mechanism in science, and radicalism in politics. Another vista that beckoned to a man of Loeb’s temper in the 1880’s was the Entwicklungsmechanik, developmental mechanics, of Wilhelm Roux. The very name was a battle cry, to storm the last refuge of biological mysticism in the name of mechanical causation. Experimental manipulation of the

embryo would perfect the mechanistic conception of the universe to which Roux was as firmly committed as Loeb. The intellectual bond between them was heightened by their common misgivings about Darwinism as the classic example of “historical” formulations in science. Roux believed in evolution, perhaps more sincerely than Loeb, but he drew a funda-

mental distinction between scientific description and causal analysis, equated historical conceptions of nature with the merely descriptive, and consigned Darwinism to this inferior

category. By contrast, he took the Newtonian science of

XX INTRODUCTION mechanics as the model for causal analysis and assimilated this to the study of the operation of mechanical forces upon the embryo. Though Roux remained a Darwinian of sorts, Ernst Haeckel as the trumpet of Darwinian orthodoxy in Germany infuriated Roux by his insistence upon the so-called ‘fundamental biogenetic law,” that development of an embryo

recapitulated the evolutionary sequence through which the species had passed. On the face of it, this was a matter for empirical resolution; and even if true perfectly compatible with the study of Entwicklungsmechanik. Roux, however, with some justification attributed to Haeckel the more ambitious design of establishing this kind of “description” not merely as valid but as exhausting the content of embryology and precluding the necessity for any mechanical analysis of development. By the same token, Haeckel was undercutting Roux’s endeavor to elevate biology to the estate of Newtonian physics. More concretely, Haeckel was pointing away from

the experimental embryology of Roux to the speculative imposition of evolutionary schemes upon the embryo; from the

microscopic slide to the hypothetical evolutionary tree.

Jacques Loeb could not hesitate for a moment between these alternatives. Though he never studied with Roux, he moved at the end of the eighties into the characteristic milieu of the developmental mechanists, the great seaside labora-

tories of marine biology which were then springing up in Western Europe and the United States, with their promise of ready access to the sea urchins and other classical organisms of embryological research. In the winter of 1889-90, Loeb was working in Naples. There he made his first significant contacts with the brilliant circle of American embryologists and cytologists, including the founder of modern genetics T. H. Morgan,

with whom he was to be associated for the remainder of his career. By 1890 he had taken an American wife, Anne Leonard —a Ph.D. in philology from Zurich—and by 1891 migrated to

America. He always said that he left Germany because he

INTRODUCTION xxl “could not live in a regime of oppression such as Bismarck had created.”? He was also an academic Jew with meager prospects of a professorial chair. In America, by contrast, he successively occupied positions at Bryn Mawr, Chicago, Berkeley, and after 1910, the Rockefeller Institute, with summers in the marine laboratories at Pacific Grove or Woods Hole.

Loeb remained fantastically, perhaps excessively, alert to every new scientific development till the day he died; but when he settled in America at the age of thirty-two, he already bore the imprint of the major influences that manifested themselves in his mature research, with the one possible exception of Arrhenius work on ionization. As a person he always remained the tense and excitable figure of his youth, short, lean, and spikey in appearance, with pointed nose and chin and

dark glinting eyes that could stab an opponent but also break up in laughter. He was an indefatigable, almost frenzied, worker, hungry for recognition and never satisfied with what he got, assailed by a perpetual sense of isolation from his peers,

biting and dogmatic in his pronouncements but prepared to seek an opponent out with an ungrudging, “You are right, I was wrong!” Ernest Rutherford on a visit to Berkeley found Loeb “rather helpless outside his lab” and tended like a child by his wife, who spoke of him in the third person as Jacques Loeb and gave him “a hot time’ when she disagreed with him.'° Il

Of Loeb’s best remembered researches, those on _heliotropism in animals began to appear as early as 1888.1! In one of his first publications he described his experiments with

certain caterpillars which normally emerge in the spring, *Duffus, “Loeb,” p. 381. *°A. S. Eve. Rutherford (Cambridge, England, 1939), pp. 149-151. ‘!These and other researches of Loeb are easily traced through the bibliography

of his scientific publications, by Nina Kobelt, appended to Osterhout, “Loeb.”

XXii INTRODUCTION climb to the tips of tree branches, and feed upon the opening buds. Loeb was infuriated by the prevailing view, sedulously propagated by “Darwinian” animal psychologists in Germany, that this conduct was the product of an infallible instinct for self-preservation. He demonstrated that if the only source of light was in the opposite direction from a supply of food, so that caterpillars must turn their backs upon one to perceive the other, they kept their heads toward the light and starved to death. They were, he said, photochemical machines enslaved to the light. In place of postulating a mysterious instinct for self-preservation, for which it was difficult to imagine a mechanistic process of hereditary transmission, one might suppose instead that the relevant heredity of the caterpillars comprised nothing more than the possession of certain photosensitive substances in the head which, if the light impinged on one side only, would create a physiological imbalance leading to discomfort and mechanical reorientation of the animal to achieve a frontal fixation upon the light, with the plane of symmetry bisecting the source of stimulation. The validity of this conception, for organisms to which it was applicable at all, Loeb bolstered by experiments with two lights and with unilateral blinding. With two lights, if the organism began to move toward one in an effort to achieve symmetrical stimulation, this was a self-defeating maneuver which could only result in asymmetrical stimulation by the other light. In the end, organisms confronted with this problem went between the lights. In unilateral blinding, photopositive organisms turned continually toward the side with vision in a vain endeavor to equalize the stimulus on the blinded side. As the balance could never be restored, the animals swung incessantly about in uncontrollable “circus movements” like mechanical acrobats. The possibility of orienting an entire collection of intact organisms by resort to the appropriate tropic stimulus, Loeb regarded as the scientific “solution of the problem of will” —‘‘forcing, by external agencies, any number of indi-

INTRODUCTION XXiil viduals of a given kind of animals to move in a definite direction by means of their locomotor apparatus.” He took delight in demonstrating that certain organisms which did not appear to be accessible to tropisms could instantly and infallibly

be rendered heliotropic and oriented in a single direction by a simple expedient like adding carbonic acid to the medium. The translation of presumably complicated instincts into

elementary tropisms only whetted Loeb’s appetite for an assault upon the crux of biological mysticism, the process of fertilization where so many ingenious theologians through the ages had seen their chance to slip a soul in while nobody was looking. Loeb ended by accomplishing artificial parthenogenesis —“the substitution,” in Loeb’s words, “of well-known physico-

chemical agencies for the mysterious action of the spermato-

zoon. This triumph was rooted in Loeb’s fascination with the work of Arrhenius upon the ionization of salts in solution. The mechanist in Loeb wanted to surmount the challenge of

fertilization. The physiologist wanted to study the effect of salt solutions upon the living cell. To test his hypothesis that salts might act upon the living organism by the combination of their ions with protoplasm, Loeb immersed fertilized eggs of the sea urchin in salt water of which the osmotic pressure had been stepped up by the addition of sodium chloride. When replaced in ordinary sea water, they underwent multicellular segmentation. Later another man repeated these experiments with magnesium chloride; and finally T. H. Morgan tried un-

fertilized eggs and found that they too could be induced to start segmentation, though without producing any larvae. For many years Morgan's disciples complained among themselves that Loeb had reaped the credit for their master’s discovery. It was Loeb, however, who succeeded in 1899 in raising the first larvae by this technique. That was the feat that captured

the imagination of the world and commenced the serious study of artificial parthenogenesis. Delage in Paris carried the demonstration one step further by bringing larvae to sexual

XXiv INTRODUCTION maturity; and Bataillon showed that frogs could be brought to maturity by merely pricking the unfertilized egg with a needle. Loeb regarded artificial parthenogenesis as the ideal means of studying the physical and chemical changes that accompany the early stages of development in the fertilized egg.

Loeb’s work on this theme greatly enhanced his repute among scientists, of whom more than one-hundred in ten countries nominated him for the Nobel Prize, though he never

received it. The newspapers made him a familiar name to the public at large, the butt of good-natured jokes and repository of pathetic hopes. Maiden ladies were said to have given up sea bathing, humorists observed that vacations at the seashore did seem to be remarkably fruitful, and barren couples wrote to Loeb in dead earnest to give them children. In the wake of this publicity, Loeb stood forth at the beginning of the twentieth century as one of the most effective spokesmen for the mechanistic conception of life. Yet he was beset from opposite sides by two formidable opponents.

In another remarkable experiment of the 1890's, Hans Driesch proffered a sensational challenge to his own master, Roux of the Entwicklungsmechanik. Roux, in keeping with his conception of embryological development as the mechanical unfolding of determinate stages with irreversible differentiation

of function among the cells, had killed one of the first two cleavage cells of a frog’s egg and verified his expectation that the surviving cell would give rise to only one half of a normal embryo. Driesch, however, announced in 1891 that with the sea urchin he had obtained complete embryos of either half-

or quarter-size depending on the cell stage when Roux’s experiment was repeated. This justly famous discovery by Driesch began as a piece of empirical research, but the more he reflected upon it, the more it seemed a colossal refutation of all mechanistic philosophies in biology. If a machine was taken apart, the individual pieces never turned into complete

INTRODUCTION XXV functioning machines of the original type. Driesch eventually

set up as a twentieth century vitalist, propounding a neoAristotelian doctrine of “entelechy.’’ He defined his entelechy

as a “suspensory power, consuming no energy but able to inhibit all the physicochemical potentialities of a cell except those that were appropriate to its ordinary business of figuring harmoniously in a complete organism. In an emergency, however, if the cell was cast adrift, all the potentialities might be unleashed and the part transformed into a whole. No mechanical phenomenon, said Driesch, could exercise these powers of discrimination.

Loeb’s paper of 1893, “On Some Facts and Principles of Physiological Morphology,” reprinted in the present volume, demonstrates that he did not originally perceive any threat to his own mechanistic position in Driesch’s experiments. He had been getting comparable results himself. When he caused recently fertilized eggs of the sea urchin to burst by placing them in dilute sea water, the extruded drop of “protoplasm” gave rise to “a normal and perfectly complete embryo,” a twin to the one that developed inside the original membrane. Loeb drew the Drieschian inference that “every part of the protoplasm” in the fertilized egg “‘may give rise to fully developed embryos without regard to preformed germ-regions.” It is clear

that the initiative in defining an antithesis between the two men lay with Driesch. Only when he had consecrated his researches to the promotion of neovitalism did Loeb as the counterprophet of mechanism feel obliged to take up a posture of hostility. In this context, it became a matter of much greater urgency than updating an old paper when Loeb in 1912 added a footnote to his communication of 1893: “In the light of more recent experiments it is possible, that after all only such pieces can develop into a normal embryo which contain the different germ-regions. In short, a cleavage cell could only tum into a

complete embryo if it got a representative selection of the physicochemical components of the fertilized egg. There was

XxXvi INTRODUCTION no entelechy in that. Yet the definitive overthrow of Drieschian neovitalism was not accomplished so much by other people’s emendation of his empirical findings as by his own increasingly mystical formulations. Most biologists took one look at these

and fled in dismay. The threat that Driesch represented to Loeb was self-liquidating. The other major antagonist of whom Loeb was conscious

at the beginning of the twentieth century was Wilhelm Ostwald, one of the great exemplars with Haeckel, Loeb, and Arrhenius of the omniscient life-style in science. As a pioneer of physical chemistry, Ostwald was one of Loeb’s idols, whom he induced to make the long trek to Berkeley in 1903 to lend

countenance to the new field in America (and incidentally, to Loeb).’* But as a man who conducted a running campaign against mechanism, Ostwald was the enemy. To those who said they could not conceive of nature except in mechanical terms, he, a doughty unbeliever, sternly repeated the Biblical Commandment: Thou shalt not make unto thee any graven image, or any likeness. Ostwald’s alternative to a mechanistic conception of the universe was a science of pure energetics, concerning itself solely with transfers of energy and rigorously avoiding the invocation of any mechanistic or material basis for these transactions. The energy concept was, or ought to be,

an escape from mechanism. Of the world riddles to which Du Bois-Reymond returned his famous [gnorabimus, Ostwald

said that they were only insoluble for men who clamped a mechanistic vise upon the human intellect. He for his part expected the intellect to be adequate to all the puzzles of nature if only liberated from the trammels of outworn dogma about the one permissible kind of scientific explanation. Unlike

the mechanistic physiologists, Ostwald was a monist who declined to accept any permanent demarcation of spheres between knowledge and faith. The whole universe under all 12For Ostwald’s own account of his visit to Berkeley, see his autobiography, Lebenslinien, 3 vols. (Berlin, 1926-1927), vol. I, ch. 14.

INTRODUCTION XXVii of its aspects could be encompassed by empirical science. Sociology could be put upon a scientific basis by defining its subject matter as the transfer of energy in human relations. The moral function of religion would be supplanted by a new ethical imperative, to waste no energy. As a monist in philosophy, a democrat in politics, and an unbeliever in religion, Ostwald was the most dangerous of all conceivable adversaries to Loeb—an antimechanist embodying the entire constellation of values which Loeb sought to invoke as the humane sanctions of mechanism. By overlapping with Loeb in everything except his mechanism, Ostwald demonstrated the adventitious nature of the links that bound Loeb’s conception of nature to the scheme of values he was endeavoring to enact in human affairs. Yet Ostwald fell into one notonious difficulty by which Loeb persuaded himself that antimechanism had failed. Ostwald and his master in philosophy Ernst Mach regarded the existence of atoms and molecules as totally unsupported by direct sensory experience. Only a dogmatic materialism, they said, could blind anybody to the true state of affairs. Accordingly, atoms and molecules could not figure in a truly scientific account of nature. Ostwald embarked upon the tour de force of writing comprehensive treatises on chemistry in which he devised more or less ingenious evasions of

the entire atomic theory. In 1909, however, in the fourth edition of his textbook on general chemistry, Ostwald capitulated. The existence of atoms, he said, had been established by

various empirical researches, including the work of Jean Perrin on Brownian motions—random motion of fine particles in suspension, attributable to molecular bombardment. Loeb regarded this admission with some complacency as the deathrattle of antimechanism.'* He spoke, as Ostwald’s own usage

justified, of “the molecular or mechanistic theory” and said that the “one solid foundation” for resistance to the mechanistic a6. nie Chanistic Science and Metaphysical Romance,” Yale Review, 4 (1915), 766-771.

XXViil INTRODUCTION conception had been lingering doubts about “the real existence of the molecules.” ““We know today not only that molecules exist, but we are able to state the exact number of molecules contained in one gram of a given substance.”

Flushed with a sense of triumph over his enemies, Loeb went to claim his victory at the First International Congress of Monists in September 1911—a veritable concourse of the omniscients convened by Ernst Haeckel at Hamburg.** To this,

the most radical, libertarian, and anti-Prussian of German cities, delegations of freethinkers, freemasons, ethical culturists, socialists, pacifists, and internationalists swarmed from many countries for a feast of reason on the edge of an abyss which they were the last people in the world to suspect. For

Loeb, these few days in Hamburg were a foretaste of the golden age, the Enlightenment come again but this time forever. In a state of fierce intoxication with his vision, he poured out “The Mechanistic Conception of Life” to an audience of several thousand. He portrayed the physicochemical explanation of life as making explosive progress in the opening decade of the twentieth century. By no coincidence, it was the period

of Loeb’s attaining his own prime as an investigator. The pieces were rapidly falling into place with his help. A dozen years before, “the activation of the egg by the spermatozoon”™

had been “shrouded in complete darkness.” Now, thanks to Loeb’s work on artificial parthenogenesis, it was “‘practically completely reduced toa physicochemical explanation.” A dozen

years before, “the field of heredity” had been “the stamping ground for the rhetorician and metaphysician.” Now, with the triumph of Mendelism, it was “the most exact and rationalistic part of biology, where facts cannot only be predicted qualitatively, but also quantitatively.” Best of all, the mysterious realm of the will had been brought within the scope of physicochemical explanations by Loeb’s work on animal 14Ostwald, Lebenslinien, vol. UI, ch. 17.

INTRODUCTION XX1ixX tropisms. The “wishes and hopes, disappointments and sufterings’ of men were grounded in instincts “comparable to the light instinct of the heliotropic animals,” and for some of these the “chemical basis” was already sufficiently understood to

make it “only a question of time’ before they were fully accounted for on mechanistic lines. Some tasks remained, above all to explain the origin of life—a favorite theme of his friend Arrhenius, another speaker at the Congress. Loeb conceived of this as an issue to be determined by efforts at the “artificial production” of life, and the latter as a thing to be speedily accomplished or shown to be impossible. In his moment of ecstatic communion with the vanguard of true believers, he was not about to sell the possibilities of science short. There was nothing, he said, to indicate that this final task was beyond the reach of twentieth-century man—man come to his full growth and realizing his potentialities for the first time.

Monists had a raw sensitivity to the charge that they were undermining ethics and morality. Loeb could not have been one of them or commanded their respect if he had failed to explore the ethical implications of the mechanistic conception of life. He ended by asking the question they dreaded to hear but were ashamed to dodge: “if we ourselves are only chemical mechanisms—how can there be an ethics for us?’ His answer was that we approve what instinct compels us “machine-like”’ to do. Yet the point of ethics is to make discriminations. Loeb must explain how some people and actions came to be disap-

proved. A thoroughly naturalistic account would have been that men try to enforce their instinctive preferences upon each other, and where they differ engage in the mutual recrimination called ethics, with no objective means of deciding between them. This position would have been totally unaccept-

able to Loeb. He wanted to establish ethical absolutes of

universal validity—the “instinct of workmanship” borrowed from his friend Thorstein Veblen, the love of a mother for

XXX INTRODUCTION her children, the “struggle for justice and truth” arising out of the compulsion “to see our fellow beings happy.” The severely telescoped argument by which Loeb in his peroration at Hamburg endeavored to salvage a universal ethic turned upon three unspoken and perhaps unconscious postulates—that there is a determinate number of instincts; that none of these are bad per se; and that there is no inherent tendency toward imbalance or conflict among them. Within these bounds, Loeb the scientist defined a biological form of ethical deficiency, when “‘mutant”’ individuals occurred, lacking

one or more instincts. Loeb the socialist defined a sociological form of ethical inferiority, when “‘economic, social, and political conditions or ignorance and superstition may warp or

inhibit the inherited instincts and thus create a civilization with a faulty or low development of ethics.’ Here Loeb was caught in the same trap as Condorcet at the end of the Enlightenment and many socialists in the nineteenth century. To preserve his ultimate ethical criterion of unimpeded expression of the natural man, he had to deny that instincts can generate the institutions that warp them. Loeb intended his address as a Sursum Corda to lift the audience onto the same plane of exaltation as himself. The chairman of the meeting chose to think instead that Loeb had shocked and frightened the audience by his “harshness” and fanaticism and made it necessary for somebody to get the

Congress off the shoals that Loeb had driven it upon. The chairman thought that he was the man. He painted in retrospect a dramatic contrast between Loeb and himself—Loeb, pale, slight, and dark-haired, driving home a “‘lifeless” conception of life with merciless hammerblows, reckless of the consequences; followed by a stocky comfortable-looking man, and blond to lighten the gloom, equally scientific but warm and personal in his conception of science as incorporating all the traditional values of religion and culture and able to make the audience in love with science again after Loeb had made them almost afraid of it.

INTRODUCTION XXxi The blond chairman was Wilhelm Ostwald. He had lent his name and presence to Haeckel’s Congress precisely to salvage monism from what he regarded as the ruins of an antiquated materialism espoused by the mechanists. In chairing Loeb’s address, he would have been less than human if his general hostility to mechanism had not been sharpened by his recent experience of being gloated over by the mechanists for his enforced retreat on atoms. The fear of Loeb which Ostwald

professed to detect in the audience may well have been a projection of his own soreness. Loeb had the sense of communicating his enthusiasm to a particularly receptive group. He continued to think that Ostwald’s guns had been spiked for good by the triumph of atomism. When in 1912 Loeb took his Hamburg address as the title-

piece for the present volume, he could feel that he was in sight of the promised land. He did not have long to cherish the mirage. The outbreak of the First World War came as an

incredible shock to a socialist and humanitarian who had always identified the advance of the mechanistic conception not merely with the accumulation of scientific discoveries but with the general progress of enlightenment envisioned by the eighteenth-century philosophers.*? Now he saw a “wave of

homicidal emotion” sweeping over the world, by which “tolerance, justice, and gentleness’’ were hopelessly engulfed. All the “mediaeval forces” that had no business surviving into

the twentieth century were more firmly in the saddle than ever—rulers, adventurous politicians, the military caste, armament mongers, prospective army contractors, international traders,” aided and abetted by their kept historians and literary men. Loeb’s bitterness was compounded by his conviction that most German socialists had been duped into supporting the war by playing upon their racial antipathy to the Slavs. Loeb emphasized that Americans were open to the same appeals to racism, as demonstrated by the refusal of 15*“Freedom of Will’; Duffus, “Loeb,” pp. 380-381.

XXxXil INTRODUCTION labor unionists to work with Orientals and Negroes. He warned against ““a future militaristic government” hurling the Americans against Japan in a war of races. To give a final twist to Loeb’s anxiety, the war struck the most ambiguous echoes from his own research. He instinctively

described the evils of the war in terms of animal tropisms. The flocking of men to the armies under the goad of racism was like the mechanical alignment of crustaceans by light. The great evil of militarism in general was the reduction of men to the “status of reflex machines.” It was curious language from a man who had rejoiced in smashing the delusion of individual freedom. When he said that the war made him “literally sick,”’

we may well suspect that he was sick in a way that only he could know, from a moment of appalling truth about his life’s endeavor.

By 1915 Loeb had sufficiently recovered his élan to say that whatever limited progress humanity had made to date— “not only in physical welfare but also in the conquest of superstition and hatred, and in the formation of a correct view of life’’—it owed to mechanistic science.’° That was still the

| only hope for the future. On these contracted terms, he kept his old faith alive; but his momentary expectation of the millennium was dead. As he poignantly wrote to Arrhenius after the war: “I wish something might be done to make the world a little more promising for the next years, but the outlook is bad. Personally I work hard because I want to forget, and I am very grateful to science that it permits us to forget a good deal of the outside world.” ** He was then prosecuting distinguished researches on the colloids, which any other scientist might have regarded as crowning his career; but for Loeb it was utter defeat to be saying at the end of his days that he valued science as an escape from the world rather than a means of dominating it. 16**Mfechanistic Science and Metaphysical Romance,” p. 785. 17Quoted in Duffus, “Loeb,” p. 381.

INTRODUCTION XXXlii Though Loeb entered the 1920’s in a chastened mood, this proved ironically to be the period of his greatest popular vogue. He had lived into a decade when orthodox faiths were on the run and idealistic philosophies in disrepute. The very expansiveness of his life-style in science—his willingness to tackle the layman’s own perplexities—made him accessible to the general imagination in a way that more austere investigators could never be. He came to figure among the heroes of the

intelligentsia with Veblen (his friend and correspondent), Mencken (who admired him), and Sinclair Lewis. When Lewis sent Martin Arrowsmith to the gravest encounter of his life,

he had him swear “by Jacques Loeb.” Under the guise of “Max Gottlieb,” Lewis drew upon Loeb to portray Arrowsmith’s own master in science and the only model for a life of integrity and fulfillment that could stand the acid scrutiny of the debunkers.1® Lewis was initiated into the cult of Loeb by Loeb’s former student Paul de Kruif, then commencing his career as a popularizer of science. De Kruif and other journal-

ists of the early twenties promoted Loeb to the ranks of Galileo, Newton, and Darwin.’ Though few if any scientists would have gone this far and some were envenomed detractors of Loeb, many paid tribute to him on his death in 1924 as one of the legendary experimentalists and seminal thinkers in the history of biology.*° ree

The question becomes how Loeb and his work have stood up under the scrutiny of another forty years. Research on artificial parthenogenesis has continued to flourish.*! Discussion 18Mark Schorer, Sinclair Lewis (New York, 1961), p. 418. 19See De Kruif, “Loeb,” and Duffus, “Loeb.” “0Robertson, ““Loeb’’; Osterhout, “Loeb.”

“IR. A. Beatty, Parthenogenesis and Polyploidy in Mammalian Development (Cambridge, England, 1957); Lord Rothschild, Fertilization (London, 1956); C. R.

Austin, The Mammalian Egg (Oxford, 1961). Artificial parthenogenesis in sea urchins: Ethel Browne Harvey, The American Arbacia and Other Sea Urchins (Princeton, 1956).

XXXivV INTRODUCTION of the relevant findings is complicated by the fact that workers in the field differ in their use of the term “parthenogenesis. Some confine it to the production—without genetic participation by a male—of a complete organism brought to birth. Others apply it to any stage in such a process of development, however rudimentary. Rudimentary parthenogenesis has been artificially induced, more readily in echinoderms and amphibians but in mammals as well, by a whole battery of techniques—hyper- and hypotonic solutions as indicated by Loeb; cold shock; heat shock; anaesthetization; culture in vitro; and ““gynogenesis, activation of the egg by sperm either of the same or different species, with the gene complement of the sperm knocked out by x-rays, ultra-violet rays, or chemicals, so that only the maternal genes can operate. The opposite phenomenon of “androgenesis’—loss or inactivation of the maternal chromosomes and derivation of the gene complement exclusively from the sperm—has been artificially induced in amphibians.

By far the most sensational results with artificial parthenogenesis in mammals were reported by Gregory Pincus in 1939 and 1940. Pincus claimed to have brought no fewer than 7 parthenogenetic mammals to birth—4 chinchilla and 3 rabbits—by three basic techniques. Five of his alleged succes-

ses have been generally credited—one dead female rabbit born after treating 147 eggs with hypotonic solutions and transferring the eggs into 6 host females; 2 live female chinchilla, of which one was fertile, produced by subjecting 18 ova

successively to hypotonic salts, serum, and hypertonic salts

and transferring the ova to a host female; one live female rabbit born after culturing 252 eggs in vitro and transferring them to 5 host females; and one live female rabbit born after placing a cooling jacket around the Fallopian tube of a virgin doe and allowing the embryo to proceed to term in situ. In each instance, males were totally excluded from contact with the female donors and hosts at every stage. Pincus was and

INTRODUCTION XXXV remained a reputable scholar, but independent confirmation of his results was extremely slow in coming. In 1949 Thibault by use of Pincus’ technique for chilling unfertilized rabbit eggs in situ produced a 67/,-day blastocyst in the process of implanting itself. Chang in 1952 by chilling unfertilized rabbit eggs

in vitro and transferring them to host females brought 16% of the eggs to the 2-7 cell stage and another 6% to the 8-32 cell stage. None of the blastocysts gave any sign of implanting

themselves. The limited success achieved by Thibault and Chang cannot be regarded as a refutation of Pincus’ claims to have brought parthenogenetic mammals to actual birth. They did not conduct their experiments on a large enough scale to make the duplication of his results probable. Parthenogenesis belongs to a wide spectrum of theoretically conceivable “routes of development.’’** Loeb by his pioneering research on one of these gave a fundamental stimulus to experimental induction of the others. Two principal kinds of insight have followed—correlation of aberrant development with abnormal cytology; and sharper delineation of the evolutionary gain from normal development. The very difficulty

in sustaining artificial development along the less eligible routes has underscored the survival value of following the main road. Yet some investigators have argued that the main routes themselves may have evolved by natural induction of aberrant pathways of development similar to those contrived by scientists, but in circumstances making for an evolutionary advantage. Loeb by triggering research in this general area unwittingly helped to bring evolutionary science within the scope of laboratory experimentation in the way that he had regarded as necessary to make it truly scientific. Loeb’s principal theoretical construction, the doctrine of animal tropisms, necessarily cut across the labors of the two great pioneers of comparative psychology, C. Lloyd Morgan “A concept developed by Beatty.

XXXVi INTRODUCTION in England and E. L. Thorndike in the United States. They agreed with him in despising the sentimental Darwinism that lavished human attributes upon animals. Yet in retrospect they can be seen preparing the way for a fundamental attack upon tropisms. Here they were elaborating upon a hint thrown

out by Herbert Spencer, that a chance reaction to a given stimulus by producing a pleasurable outcome might become habitual. By a kind of neural facilitation, a physiological groove

would be worn in which energy would tend to flow whenever the stimulus recurred. Lloyd Morgan in 1894 and Thorndike in his monograph on Animal Intelligence of 1898 sharpened

the edge of this concept by giving it a name—learning by “trial and error.” Thorndike supplied classic experimental demonstrations of what he meant. He showed that (uninitiated) cats who must claw a string or loop to get out of a box and obtain food reacted at random from their standard reper-

tory of motions till they blundered upon the solution. The successful pattern of behavior, he said, got “stamped in” retroactively by the pleasure it induced. The man who turned the concept of trial and error against Loeb was the American biologist Herbert Spencer Jennings.”° Jennings began his brilliant researches on the behavior of lower organisms—chiefly bacteria, Protozoa, and the lower Metazoa— as early as 1896. He always conceived of his own career as a

continuation of the impulse given by Loeb to the objective analysis of behavior. This did not deter him from drawing upon Lloyd Morgan and Thorndike to demolish Loeb’s doctrine

of animal tropisms. In his principal book, Behavior of the Lower Organisms of 1906, Jennings did not deny that a few organisms answered fairly well to Loeb’s expectations. Jennings also discovered certain organisms which responded to unfavor-

able stimulation by perpetually turning in a given direction; 3Qn Jennings’ relation to Loeb, see Donald D. Jensen, “Foreword,” H. S. Jennings, Behavior of the Lower Organisms (Ist ed. 1906; facsimile ed. 1962, Bloomington, Indiana), ix-xvii.

INTRODUCTION XXXvii but these “avoiding reactions,’ though superficially resembling Loebian tropisms, were exactly the opposite. All unpleasant

stimuli elicited the same reaction, without any specificity whatever, and the organism always turned in the same direction regardless of the direction from which the stimulus was

applied. Avoiding reactions, though not tropistic, were at any rate predictable. Jennings demonstrated, however, that many of the lower organisms did not initially respond to an unfamiliar stimulus in any determinate way. Instead they engaged at random in their usual spontaneous activities till they chanced upon some course of action that relieved the discomfort induced by the stimulus. Trial and error extended to the lowest reaches of the animal kingdom. Thorndike and Jennings between them had supplied the equivalent for animals of the Darwins’ discovery of circumnutation in plants— that reactions to external stimuli were superimposed upon a ground of spontaneous movements. As circumnutation had been anathema to Loeb’s master Sachs, trial and error became an

object of derision to Loeb. But the scientific community increasingly followed Jennings.

Jennings did not regard his refutation of Loeb on tropisms as a blow at determinism. He professed to be as much of a

determinist as Loeb, and took pains to dissociate himself from Drieschian neovitalism. Where they differed was in Jennings conviction that determinism need not be confined to the irresistible impact of stimuli upon inert organisms but might equally comprehend the internal physiological constraint

that bore the guise of spontaneous activity when observed from without. Jennings held that biological “spontaneity,” as in learning by trial and error, was itself fully determined by physicochemical reactions within the organism. True determinism was a product of the interaction between external stimulus and inwardly conditioned behavior. Unlike Jennings, his chief disciple $. O. Mast took a highly

permissive attitude toward vitalism, declined to rule out

XXXVili INTRODUCTION Driesch’s entelechies as unscientific, and evinced a strong personal, professional, and philosophical animus against Loeb. With obsessional tenacity and venomous glee, Mast devoted

a long life to piling up mountains of evidence against Loeb on tropisms. By 1940 Fraenkel and Gunn could record in their Orientation of Animals that the doctrine of animal tropisms as a principle of general applicability was dead.** They rightly regarded Mast as the chief agent of its demise, the man who completed the work that Jennings began. Yet Loeb had bred his own corrective by transmitting through Jennings to Mast

the very impulse that proved him wrong. Jennings, a more generous spirit than Mast, did not fail in rebutting Loeb on tropisms to recall his lasting contribution to the scientific study of behavior.*? Everyone, he said, must recognize “the tremendous service done by Loeb in championing through thick and thin the necessity for the use of objective, experimental factors in the analysis of behavior.” No experimentalist, knowing the previous history of the subject, could reread Loeb’s early work on behavior without being filled with admiration for “the clear-cut enunciation, defense, and application

of the principles on which valuable experimental work has rested since that time, and on which it must continue to rest.”’ It was a remarkable tribute from one of the best judges. Jennings, Mast, and Loeb, for all their differences, were alike in aspiring to the ultimate truth about animal behavior rather than glimpses of the truth eked out by working postulates. Yet this aspiration had been bypassed as early as 1894 by Lloyd Morgan’s famous “canon of parsimony’ —“In no case

may we interpret an action as the outcome of the exercise of a higher psychical faculty, if it can be interpreted as the outcome of the exercise of one which stands lower in the psychological scale.’’?° Lloyd Morgan’s canon was a form of Occam’s 24Gottfried S. Fraenkel and Donald L. Gunn, The Orientation of Animals (Oxford, 1940; 2d ed. New York, 1961). 2°Quoted from Jennings, 1908, by Jensen, “Foreword.” 26C. Lloyd Morgan, An Introduction to Comparative Psychology (London, 1894), p. 93.

INTRODUCTION XXxXix razor, slicing away sentimental Darwinism. In this sense, it harmonized to perfection with Loeb’s own attitude. On a deeper level, it outraged the faith that drove him by substituting

a mere rule of convenience and canon of simplicity for what had been in Loeb a dogmatic affirmation of the truth. More generally, Loeb’s entire posture in science was outflanked by a tremendous shift from mechanism as truth and metaphysic to mechanism as postulate and strategy. Lloyd Morgan's approach to animal psychology fell in with a rising temper in the Western world that found its most compact expression in Hans Vaihinger’s philosophy of “‘as if’—actually

enunciated in a dissertation of 1876 but first published in 1911.°’ Vaihinger argued that science advances by deliberately positing assumptions that cannot be verified—“‘fictions,”’ which do not permit of either proof or disproof, as distinguished from “hypotheses, which do—but nevertheless serve as instruments

of thought by which verifiable knowledge is attained. The atom, he said, is a fiction, abundantly justified by the results of invoking it, but neither the genuine entity affirmed by the mechanists nor the unscientific fantasy castigated by antimechanists. Vaihinger did not refer to Loeb or Ostwald, but men of either temper stood equally arraigned as naive at the bar of as-if—Loeb who dogmatically affirmed the existence

of atoms, Ostwald who reprobated them even as a mere expedient of thought; Loeb who said the body simply was a machine, Ostwald who forbade the scientist even to deal in mechanical images. The philosophy of as-if renewed the license

to think in mechanical terms which Ostwald had tried to suppress. But equally it called in question the perfect “fit” and metaphysical identity between machine and biological organism which Loeb had postulated. The mechanistic approach became an approximating engine—not a metaphysic at all but a tool of thought. By the middle of the twentieth century, the prevailing mode “"See the autobiographical essay by Vaihinger in The Philosophy of “As If,” trans. C. K. Ogden (2d Eng. ed. from 6th German; London, 1935).

x | INTRODUCTION of as-if in biology as elsewhere had become the construction of “models” to match against the complexity of the living organism. Many of these were unabashedly mechanical—electrical circuits, real or imaginary, and actual functioning electronic “animals.” Jacques Loeb was most in league with the future in a passage of 1915 where he must have seemed to contemporary critics to be grasping at crude analogies: In the case of heliotropic reactions, the mechanist welcomes the news that John Hays Hammond, Jr. has succeeded in constructing

heliotropic machines. He has invented a torpedo which can be directed by a searchlight like a negatively heliotropic animal, and he has also constructed a “heliotropic’ dog which follows a lantern in the dark like the positively heliotropic caterpillar. The eyes of the

“dog” are of selenium, separated from each other by a wooden board which represents the nose, and allows one eye to receive light

while the other is shaded. The electric resistance of selenium is altered by light; and when one selenium eye of the “dog” is shaded, while the other is illuminated, the electric energy which moves the wheels that take the place of the normal dog’s legs, no longer flows symmetrically to the wheels on both sides, and the “dog” turns in the direction of and follows the lantern. Here we have a model of the heliotropic animal, whose purely mechanistic character is beyond suspicion.”®

Even in this context, Loeb could never strike the note of as-if, the deliberate evasion of metaphysical issues, by which the cyberneticians of the 1950’s and ‘60's got the advantage of mechanism without the trouble of defending it. Yet the rise and persistence of as-if was not the whole story of mechanistic thought in the twentieth century. As the metaphysical brand of mechanism had been undercut by as-if, so the ontological evasion of the latter was undercut in turn by the explosion in the biochemistry of genetics after 1944. In studying the organism in being, it might still be necessary to 28‘Nfechanistic Science and Metaphysical Romance,” pp. 780-781. Hammond was a celebrated mining engineer of the general vintage of Herbert Hoover.

a

INTRODUCTION xli

conceive of mechanical models as no more than crude approximations to biological reality. But not if one reverted to

the chromosomes with the men who were cracking the genetic code. There no ontological evasion seemed necessary or even permissible. The genes were simply physicochemical units of which the constitution and properties were increasingly known. Seen in this perspective, the actual organism might experience a complex interplay between genotype and environment but could hardly transcend its purely physicochemical origins. Here

again Jacques Loeb can be seen reaching out to the future

and shrewdly fixing upon the premonitions of a biochemistry of genetics that were available to a man of his time. He said

in 1911 that the main task for students of heredity was to determine “the chemical substances in the chromosomes which

are responsible for the hereditary transmission of a quality” and “the mechanism by which these substances give rise to the hereditary character.” It was a plea for the discovery of DNA.

Though the biochemistry of genetics when it finally materialized lent a new credibility to Loeb’s brand of mechanism,

the continuing pertinence of the animus he projected did not really require the predominance of one kind of mechanism over the other. To act as if the organism is a machine and to act because it is are operationally identical; and it is the only operation that is open to an experimentalist. At the moment

of closing with the organism in an experiment—of coming alive as an investigator—every biologist recovers the posture of Loeb. It is the only posture that will make biology go at the moment of truth. DONALD FLEMING

xlii INTRODUCTION A NOTE ON THE TEXT

The text is taken verbatim from the only previous edition in English (University of Chicago Press, 1912). There was a French edition in 1914

(Félix Alcan, Paris). Brief technical notes have been appended to the individual essays, to indicate the present state of knowledge on the issues discussed by Loeb. The original index has been keyed to the new edition.

THE MECHANISTIC CONCEPTION

OF LIFE

PREFACE

Tue essays contained in this volume were written on different occasions mostly in response to requests for a popular presentation of the results of the author's investigations. The title of the volume characterizes their general tendency as an attempt

to analyze life from a purely physico-chemical viewpoint. Since they deal to a large extent with the personal work of the author, repetition was unavoidable, but in view of the technical dificulties presented by some of the topics this may serve to facilitate the understanding of the subject. The author wishes to thank the editors and publishers who gave their consent to the reprinting of these essays: Professor J. McKeen Cattell, of Columbia University, Professor Albert Charles Seward, of the University of Cambridge, England, Ginn & Co., of Boston, G. P. Putnam’s Sons, of New York and

London, and the J. B. Lippincott Company, Philadelphia. THE ROCKEFELLER INSTITUTE FOR MEDICAL RESEARCH

April 4, 1912

i THE MECHANISTIC CONCEPTION OF LIFE

I. INTRODUCTORY

Ir is the object of this paper to discuss the question whether our present knowledge gives us any hope that ultimately life, ie., the sum of all life phenomena, can be unequivocally explained in physico-chemical terms. If on the basis of a serious survey this question can be answered in the affirmative our social and ethical life will have to be put on a scientific basis and our rules of conduct must be brought into harmony with the results of scientific biology.

It is seemingly often taken for granted by laymen that “truth” in biology, or science in general, is of the same order as “truth” in certain of the mental sciences; that is to say, that

everything rests on argument or rhetoric and that what is regarded as true today may be expected with some probability to be considered untrue tomorrow. It happens in science,

especially in the descriptive sciences like paleontology or zoology, that hypotheses are forwarded, discussed, and then abandoned. It should, however, be remembered that modern biology is fundamentally an experimental and not a descriptive science; and that its results are not rhetorical, but always assume one of two forms: it is either possible to control a life

phenomenon to such an extent that we can produce it at desire (as, e.g., the contraction of an excised muscle); or we Address delivered at the First International Congress of Monists at Hamburg, september 10, 1911; reprinted from Popular Science Monthly, January, 1912, by courtesy of Professor J. McKeen Cattell.

5

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6 Tse MEcuanistic CoNCEPTION OF LIFE

succeed in finding the numerical relation between the con-

ditions of the experiment and the biological result (e.g., Mendel's law of heredity). Biology as far as it is based on these

two principles cannot retrogress, but must advance. II. THE BEGINNING OF SCIENTIFIC BIOLOGY

Scientific biology, defined in this sense, begins with the attempt made by Lavoisier and Laplace (1780) to show that the

quantity of heat which is formed in the body of a warmblooded animal is equal to that formed in a candle, provided that the quantities of carbon dioxide formed in both cases are identical. This was the first attempt to reduce a life phenomenon,

namely, the formation of animal heat, completely to physico-

chemical terms. What these two investigators began with primitive means has been completed by more recent investigators—FPettenkoffer and Voit, Rubner, Zuntz and Atwater. The oxidation of a food-stuff always furnishes the same amount of heat, no matter whether it takes place in the living body or outside. These investigations left a gap. The substances which undergo

oxidations in the animal body—starch, fat, and proteins—are substances which at ordinary temperature are not easily oxi-

dized. They require the temperature of the flame in order to undergo rapid oxidation through the oxygen of the air. This discrepancy between the oxidations in the living body and those in the laboratory manifests itself also in other chemical processes, e.g., digestion or hydrolytic reactions, which

were at first found to occur outside the living body rapidly only under conditions incompatible with life. This discrepancy was done away with by the physical chemists, who demonstrated

that the same acceleration of chemical reactions which is brought about by a high temperature can also be accomplished at a low temperature with the aid of certain specific substances,

the so-called catalyzers. This progress is connected pre-

THE MECHANISTIC CONCEPTION OF LIFE 7 eminently with the names of Berzelius and Wilhelm Ostwald.

The specific substances which accelerate the oxidations at body temperature sufficiently to allow the maintenance of life are the so-called ferments of oxidation.

The work of Lavoisier and Laplace not only marks the beginning of scientific biology, it also touches the core of the problem of life; for it seems that oxidations form a part, if not the basis, of all life phenomena in higher organisms. Il]. THE “RIDDLE OF LIFE™

By the “riddle of life’? not everybody will understand the same thing. We all, however, desire to know how life originates and what death is, since our ethics must be influenced to a large extent through the answer to this question. We are not yet able to give an answer to the question as to how life originated on the earth. We know that every living being is able to transform food-stuffs into living matter; and we also know that not only the compounds which are formed in the animal body can be produced artificially, but that chemical reactions which take place in living organisms can also be repeated at the same rate and temperature in the laboratory. The gap in our knowledge which we feel most keenly is the fact that the chemical character of the catalyzers (the enzymes or ferments) is still unknown. Nothing indicates, however, at present that the artificial production of living matter is beyond the possibilities of science. This view does not stand in opposition to the idea of Arrhenius that germs of sufficiently small dimensions are driven by radia-

tion-pressure through space; and that these germs, if they fall upon new cosmic bodies possessing water, salts, and oxygen, and the proper temperature, give rise to a new evolution of organisms. Biology will certainly retain this idea, but I believe that we must also follow out the other problem: namely, we

8 THE MECHANISTIC CONCEPTION OF LIFE must either succeed in producing living matter artificially, or we must find the reasons why this is impossible. IV. THE ACTIVATION OF THE EGG

Although we are not yet able to state how life originated in general, another, more modest problem, has been solved, that is, how the egg is caused by the sperm to develop into a new individual. Every animal originates from an egg and in the majority of animals a new individual can only then develop

if a male sex-cell, a spermatozoon, enters into the egg. The question as to how a spermatozoon can cause an egg to develop

into a new individual was twelve years ago still shrouded in that mystery which today surrounds the origin of life in general.

But today we are able to state that the problem of the activation of the egg is for the most part reduced to physico-chemical terms. The egg is in the unfertilized condition a single cell with only one nucleus. If no spermatozoon enters into it, it perishes after a comparatively short time, in some animals in a few hours, in others in a few days or weeks. If, however, a spermatozoon enters into the egg, the latter begins to develop,

i.e., the nucleus begins to divide into two nuclei and the egg which heretofore consisted of one cell is divided into two cells. Subsequently each nucleus and each cell divides again into two, and so on. These cells have, in many eggs, the tend-

ency to remain at the surface of the egg or to creep to the surface, and later such an egg forms a hollow sphere whose shell consists of a large number of cells. On the outer surface of this hollow sphere cilia are formed and the egg is now transformed into a free-swimming larva. Then an intestine develops

through the growing in of cells in one region of the blastula and gradually the other organs, skeleton, vascular system, etc., originate. Embryologists had noticed that occasionally the un-

fertilized eggs of certain animals, e.g., sea-urchins, worms, or even birds, show a tendency to a nuclear or even a cell

THE MECHANISTIC CONCEPTION OF LIFE 9

division; and R. Hertwig, Mead, and Morgan had succeeded in inducing one or more cell divisions artificially in such eggs. But the cell divisions in these cases never led to the development of a larva, but at the best to the formation of an abnormal mass of cells which soon perished. I succeeded twelve years ago in causing the unfertilized eggs of the sea-urchin to develop into swimming larvae by treating

them with sea-water, the concentration of which was raised through the addition of a small but definite quantity of a salt or sugar. The eggs were put for two hours into a solution the osmotic pressure of which had been raised to a certain height.

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ope oc” Fic. 1.—Unfertilized egg of the sea-urchin surrounded by spermatozoa. Only the. heads of the spermatozoa are drawn, since at the magnification used the tails were not visible.

Fic. 2,—The same egg immediately after the entrance of the spermatozoon. The egg is surrounded by a larger circle, the fertilization membrane, which is formed through the action of the spermatozoon. This formation of a fertilization membrane can be induced by a purely chemical treatment of the egg.

When the eggs were put back into normal sea-water they developed into larvae and a part of these larvae formed an intestine and a skeleton. The same result was obtained in the eggs of other animals, star-fish, worms, and mollusks. These experiments proved the possibility of substituting physico-chemical agencies for the action of the living spermato-

zoon, but did not yet explain how the spermatozoon causes the development of the egg, since in these experiments the

10 THE MECHANISTIC CONCEPTION OF LIFE action of the spermatozoon upon the egg was very incompletely

imitated. When a spermatozoon enters into the egg it causes primarily a change in the surface of the egg which results in the formation of the so-called membrane of fertilization. This phenomenon of membrane formation which had always been considered as a phenomenon of minor importance did not occur in my original method of treating the egg with hypertonic sea-water. Six years ago while experimenting on the Californian sea-urchin, Strongylocentrotus purpuratus, I succeeded in finding a method of causing the unfertilized egg to form a membrane without injuring the egg. This method consists in treating the eggs for from one to two minutes with sea-water to which a definite amount of butyric acid (or some other monobasic fatty acid) has been added. If after that time the eggs are brought back into normal sea-water, all form a fertilization membrane in exactly the same way as if a spermatozoon had entered. This membrane formation or rather the modification of the surface of the egg which underlies the

membrane formation starts the development. It does not allow it, however, to proceed very far at room temperature. In order to allow the development to go farther it is necessary to submit the eggs after the butyric acid treatment to a second operation. Here we have a choice between two methods. We can either put the eggs for about one half-hour into a hypertonic solution (which contains free oxygen); or we can put them for about three hours into sea-water deprived of oxygen. If the eggs are then returned to normal sea-water containing oxygen they all develop; and in a large number the development is as normal as if a spermatozoon had entered. The essential feature is therefore the fact that the development is caused by two different treatments of the egg; and that of these the treatment resulting in the formation of the membrane is the more important one. This is proved by the

fact that in certain forms, as for instance the star-fish, the causation of the artificial membrane formation may suffice for

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Fics. 3, 4, and 5.—Segmentation of the sea-urchin egg, resulting in the formation of two cells (Fic. 5). The changes from Fig. 3 to Fig. 5 occur in about one minute or less time. This segmentation occurs after fertilization or after the chemical treatment of the egg described in the text.

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12 THE MECHANISTIC CONCEPTION OF LIFE

the development of normal larvae; although here, too, the second treatment increases not only the number of larvae, but also improves the appearance of the larvae, as R. Lillie found. The question now arises, how the membrane formation can start the development of the egg. An analysis of the process and of the nature of the agencies which cause it yielded the result that the unfertilized egg possesses a superficial cortical layer, which must be destroyed before the egg can develop.

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Fic. 8.—Blastula. First larval stage of the sea-urchin egg. At the surface of the cells cilia are formed and the larva begins to swim and reaches the surface of the

wie 9.—Gastrula stage. The intestine begins to form and the first indication of the skeleton appears in the form of fine crystals.

It is immaterial by what means this superficial cortical layer is destroyed. All agencies which cause a definite type of cell destruction—the so-called cytolysis—cause also the egg to

develop, as long as their action is limited to the surface layer of the cell. The butyric acid treatment of the egg mentioned above only serves to induce the destruction of this cortical layer. In the eggs of some animals this cortical layer can be destroyed mechanically by shaking the egg, as A. P. Mathews

found in the case of star-fish eggs and I in the case of the eggs of certain worms. In the case of the eggs of the frog it

™ Tue MECHANISTIC CONCEPTION OF LIFE 13

suffices to pierce the cortical layer with a needle, as Bataillon found in his beautiful experiments a year ago.* The mechanism by which development is caused is apparently the same in all these cases, namely, the destruction of the cortical layer of the eggs. This can be caused generally by certain chemical means which play a role also in bacteriology; but it can also

be caused in special cases by mechanical means, such as agitation or piercing of the cortical layer. It may be mentioned parenthetically that foreign blood sera have also a cytolytic effect, and I succeeded in causing membrane formation and

in consequence the development of the sea-urchin egg by treating it with the blood of various animals, e.g., of cattle, or the rabbit.

\ 7S Fic. 10.—Pluteus stage of Strongylocentrotus purpuratus. S skeleton; D - 3D

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Recently Shearer has succeeded in Plymouth in causing a number of parthenogenetic plutei produced by my method to develop beyond the stage of metamorphosis, and Delage has reported that he raised two larvae of the sea-urchin produced by artificial parthenogenesis to the stage of sexual maturity. We may, therefore, state that the complete imita'This method does not work with the eggs of fish and is apparently as limited in its applicability as the causation of development by mechanical agitation.

14 THE MECHANISTIC CONCEPTION OF LIFE

tion of the developmental effect of the spermatozoon by certain physico-chemical agencies has been accomplished. I succeeded in showing that the spermatozoon causes the development of the sea-urchin egg in a way similar to that in my method of artificial parthenogenesis; namely, by carrying two substances into the egg, one of which acts like the butyric acid and induces the membrane formation, while the other acts like the treatment with a hypertonic solution and enables the full development of the larvae. In order to prove this for the sea-urchin egg foreign sperm, e.g., that of the star-fish,

must be used. The sperm of the sea-urchin penetrates so rapidly into the sea-urchin egg that almost always both substances get into the egg. If, however, starfish sperm is used for the fertilization of the sea-urchin egg, in a large number of cases, membrane formation occurs before the spermatozoon has found time to penetrate entirely into the egg. In consequence of the membrane formation the spermatozoon is thrown out. Such eggs behave as if only the membrane formation had been caused by some artificial agency, e.g., butyric acid. They begin to develop, but soon show signs of disintegration. If treated with a hypertonic solution they develop into larvae. In touching the egg contents the spermatozoon had a chance to give off a substance which liquefied the cortical layer and thereby caused the membrane formation by which the further entrance of the spermatozoon into the egg was prevented. H, however, the star-fish sperm enters completely into the egg before the membrane formation begins, the spermatozoon carries also the second substance into the egg, the action of

which corresponds to the treatment of the egg with the hypertonic solution. In this case the egg can undergo complete development into a larva.

F. Lillie has recently confirmed the same fact in the egg of a worm, Nereis. He mixed the sperm and eggs of Nereis and centrifuged the mass. In many cases the spermatozoa which had begun to penetrate into the egg were thrown off

THE MECHANISTIC CONCEPTION OF LIFE 15

again. The consequence was that only a membrane formation resulted without the spermatozoon penetrating into the egg. This membrane formation led only to a beginning but not to a complete development. We may, therefore, conclude that the spermatozoon causes the development of the egg in a way similar to that which takes place in the case of artificial parthenogenesis. It carries first a substance into the egg which destroys the cortical layer of the egg in the same way as does butyric acid; and secondly a substance which corresponds in its effect to the influence of the hypertonic solution in the seaurchin egg after the membrane formation. The question arises as to how the destruction of the cortical layer can cause the beginning of the development of the egg. This question leads us to the process of oxidation. Years ago I had found that the fertilized sea-urchin egg can only develop in the presence of free oxygen; if the oxygen is completely withdrawn the development stops, but begins again promptly as soon as oxygen is again admitted. From this and similar experiments I concluded that the spermatozoon causes the development by accelerating the oxidations in the egg. This conclusion was confirmed by experiments by O. Warburg and by Wasteneys and myself in which it was found that through the process of fertilization the velocity of oxidations in the egg is increased to four or six times its original value. Warburg was able to show that the mere causation of the membrane formation by the butyric acid treatment has the same accelerating effect upon the oxidations as fertilization.

What remains unknown at present is the way in which the destruction of the cortical layer of the egg accelerates the

oxidations. It is possible that the cortical layer acts like a solid crust and thus prevents the oxygen from reaching the surface of the egg or from penetrating into the latter sufficiently rapidly. The solution of these problems must be reserved for further investigation. We therefore see that the process of the activation of the

16 THE MECHANISTIC CONCEPTION OF LIFE egg by the spermatozoon, which twelve years ago was shrouded in complete darkness, is today practically completely reduced

to a physico-chemical explanation. Considering the youth of experimental biology we have a right to hope that what has been accomplished in this problem will occur in rapid succession

in those problems which today still appear as riddles. V. NATURE OF LIFE AND DEATH

The nature of life and of death are questions which occupy the interest of the layman to a greater extent than possibly any other purely theoretical problem; and we can well understand that humanity did not wait for experimental biology to furnish an answer. The answer assumed the anthropomorphic form characteristic of all explanations of nature in the prescientific period. Life was assumed to begin with the entrance of a “life principle” into the body; that individual life begins with the egg was of course unknown to primitive or prescientific man. Death was assumed to be due to the departure of this “‘life principle” from the body. Scientifically, however, individual life begins (in the case of the sea-urchin and possibly in general) with the acceleration of the rate of oxidation in the egg, and this acceleration begins after the destruction of its cortical layer. Life of warmblooded animals—man included—ends with the cessation of oxidation in the body. As soon as oxidations have ceased for some time, the surface films of the cells, if they contain enough

water and if the temperature is sufficiently high, become permeable for bacteria, and the body is destroyed by microorganisms. The problem of the beginning and end of individual life is physico-chemically clear. It is, therefore, unwarranted to continue the statement that in addition to the acceleration of oxidations the beginning of individual life is determined by the entrance of a metaphysical “life principle” into the egg; and that death is determined, aside from the cessation of oxi-

THe MECHANISTIC CONCEPTION OF LIFE 17

dations, by the departure of this “principle” from the body. In the case of the evaporation of water we are satisfied with the explanation given by the kinetic theory of gases and do not demand that—to repeat a well-known jest of Huxley— the disappearance of the “aquosity” be also taken into consideration. VI. HEREDITY

It may be stated that the egg is the essential bearer of heredity. We can cause an egg to develop into a larva without sperm, but we cannot cause a spermatozoon to develop into a larva without an egg. The spermatozoon can influence the form of the offspring only when the two forms are rather closely related. If the egg of a sea-urchin is fertilized with the sperm

from a different species of sea-urchin, the larval form has distinct paternal characters. If, however, the eggs of a seaurchin are fertilized with the sperm of a more remote species, e.g., a Star-fish, the result is a sea-urchin larva which possesses no paternal characters, as I found and as Godlewski, Kupelwieser, Hagedoorn, and Baltzer were able to confirm. This fact has some bearing upon the further investigation of heredity, inasmuch as it shows that the egg is the main instrument of heredity, while apparently the spermatozoon is restricted in the transmission of characters to the offspring. If the difference

between spermatozoon and egg exceeds a certain limit the hereditary effects of the spermatozoon cease and it acts merely as an activator to the egg.

As far as the transmission of paternal characters is concerned, we can say today that the view of those authors was correct who, with Boveri, localized this transmission not only in the cell nucleus, but in a special constituent of the nucleus, the chromosomes. The proof for this was given by facts found

along the lines of Mendelian investigations. The essential law of Mendel, the law of segregation, can in its simplest form

18 THe MECHANISTIC CONCEPTION OF LIFE be expressed in the following way. If we cross two forms which

differ in only one character every hybrid resulting from this union forms two kinds of sex-cells in equal numbers; two kinds

of eggs if it is a female, two kinds of spermatozoa if it is a

male. The one kind corresponds to the pure paternal, the other to the pure maternal type. The investigation of the structure and behavior of the nucleus showed that the possibility for such a segregation of the sex-cells in a hybrid can easily be recognized during a given stage in the formation of the sex-cells, if the assumption is made that the chromosomes are the bearers of the paternal characters. The proof for the correctness of this view was furnished through the investigation of the heredity of those qualities which occur mainly in one sex; e.g., color blindness which occurs preeminently in the male members of a family. Nine years ago McClung published a paper which solved

the problem of sex determination, at least in its essential feature. Each animal has a definite number of chromosomes in its cell nucleus. Henking had found that in a certain form of insects (Pyrrhocoris) two kinds of spermatozoa exist which

differ in the fact that the one possesses a nucleolus while the other does not. Montgomery afterward showed that Henking’s nucleolus was an accessory chromosome. McClung first expressed the idea that this accessory chromosome was connected with the determination of sex. Considering the importance of this idea we may render it in his own words: A most significant fact, and one upon which almost all investigators

are united in opinion, is that the element is apportioned to but onehalf of the spermatozoa. Assuming it to be true that the chromatin

is the important part of the cell in the matter of heredity, then it follows that we have two kinds of spermatozoa that differ from each other in a vital matter. We expect, therefore, to find in the offspring two sorts of individuals in approximately equal numbers, under normal conditions, that exhibit marked differences in structure. A careful consideration will suggest that nothing but sexual characters

nS THe MECHANISTIC CONCEPTION OF LIFE 19

thus divides the members of a species into two well-defined groups, and we are logically forced to the conclusion that the peculiar chromosome has some bearing upon the arrangement.

I must here also point out a fact that does not seem to have the recognition it deserves; viz., that if there is a cross-division of the chromosomes in the maturation mitoses, there must be two kinds

of spermatozoa regardless of the presence of the accessory chromosome. It is thus possible that even in the absence of any specialized

element a preponderant maleness would attach to one-half of the spermatozoa, due to the “qualitative division of the tetrads.”

The researches of the following years, especially the brilliant work of E. B. Wilson, Miss Stevens, T. H. Morgan, and others,

have amply confirmed the correctness of this ingenious idea and cleared up the problem of sex determination in its main features.

According to McClung each animal forms two kinds of spermatozoa in equal numbers, which differ by one chromosome. One kind of spermatozoa produces male animals, the other female animals. The eggs are all equal in these animals. More recent investigations, especially those of E. B. Wilson, have shown that this view is correct for many animals. While in many animals there are two kinds of spermatozoa and only one kind of eggs, in other animals two kinds of eggs and only one kind of spermatozoa are formed, e.g., sea-urchins and certain species of birds and of butterflies (Abraxas). In these animals the sex is predetermined in the egg and not in the spermatozoon. It is of interest that, according to Guyer, in the human being two kinds of spermatozoa exist and only one kind of eggs; in man, therefore, sex is determined by the spermatozoon. How is sex determination accomplished? Let us take the case which according to Wilson is true for many insects and according to Guyer for human beings, namely, that there are two kinds of spermatozoa and one kind of eggs. According to Wilson all unfertilized eggs contain in this case one so-called

a ve 4 X., aX\ a. a

20 THE MECHANISTIC CONCEPTION OF LIFE

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Fics. 11-16 (after E. B. Wilson).—Diagrammatic presentation of sex determination in an insect (Protenor). a a are the nuclei of unfertilized eggs. Each contains one sex chromosome marked X; the other six dark spots are the chromosomes which are supposed to transmit hereditary characters not connected with sex. b and c represent the two different types of sperm; b containing a sex chromosome X, c being without such a chromosome. d represents the constitution of the egg nucleus after it is fertilized by a spermatozoon of the type b containing a sex chromosome. This egg now has two sex chromosomes and therefore will give rise to a female. e represents a fertilized egg after a spermatozoon of the type c (without a sex chromosome) has entered it. This egg contains after fertilization only one sex chromosome X and hence will give rise to a male.

sex chromosome, the X-chromosome. There are two kinds of spermatozoa, one with and one without an X-chromosome. Given a sufficiently large number of eggs and of spermatozoa,

one-half of the eggs will be fertilized by spermatozoa with and one-half by spermatozoa without an X-chromosome. Hence

one-half of the eggs will contain after fertilization two Xchromosomes each and one-half only one X-chromosome each.

The eggs containing only one X-chromosome give rise to males, those containing two X-chromosomes give rise to females—as Wilson and others have proved. This seems to be

THE MECHANISTIC CONCEPTION OF LIFE 21

a general law for those cases in which there are two kinds of spermatozoa and one kind of eggs. These observations show why it is impossible to influence the sex of a developing embryo by external influences. If, for

example, in the human being a spermatozoon without an X-chromosome enters into an egg, the egg will give rise to a boy, but if a spermatozoon with an X-chromosome gets into the egg the latter will give rise to a girl. Since always both kinds of spermatozoa are given off by the male it is a mere matter of chance whether a boy or a girl originates; and it agrees with the law of probability that in a large population the number of boys and girls born within a year is approximately the same.” These discoveries solved also a series of other difficulties. Certain types of twins originate from one egg after fertilization.

Such twins have always the same sex, as we should expect, since the cells of both twins have the same number of Xchromosomes.

In plant lice, bees, and ants, the eggs may develop with and without fertilization. It was known that from fertilized eggs in these animals only females develop, males never. It was found that in these animals the eggs contain only one sex chromosome; while in the male are found two kinds of spermatozoa, one with and one without a sex chromosome. For Phylloxera

and Aphides it has been proved with certainty by Morgan and others that the spermatozoa which contain no sex chromosome cannot live, and the same is probably true for bees and

ants. If, therefore, in these animals an egg is fertilized it is always done by a spermatozoon which contains an X-chromosome. The egg has, therefore, after fertilization in these animals always two X-chromosomes and from such eggs only females can arise. “It is stated that the number of males born exceeds that of the females by a slight percentage. If this statement is correct it must be due to a secondarv cause, e.g., a greater motility or greater duration of life of the male spermatozoon. Further researches will be needed to clear up this point.

22 THE MECHANISTIC CONCEPTION OF LIFE

It had been known for a long time that in bees and ants the unfertilized eggs can also develop, but such eggs give rise

to males only. This is due to the fact that the eggs of these animals contain only one X-chromosome and from eggs with

only one chromosome only males can arise (at least in the case of animals in which the male is heterozygous for sex). The problem of sex determination has, therefore, found a simple solution, and simultaneously Mendel’s law of segregation also finds its solution.

In many insects and in man the cells of the female have two sex chromosomes. In a certain stage of the history of the egg one-half of the chromosomes leave the egg (in the form

of the “polar-body”) and it keeps only half the number of chromosomes. Each egg, therefore, retains only one X or sex chromosome. In the male the cells have from the beginning only one X-chromosome and each primordial spermatozoon divides into two new (in reality into two pairs of) spermatozoa, one of which contains an X-chromosome while the other is without such a chromosome. What can be observed here directly

in the male animal takes place in every hybrid; during the critical, so-called maturation division of the sexual cell in the hybrid, a division of the chromosomes occurs, whereby only one-half of the sex-cells receive the hereditary substance in regard to which the two original pure forms differ. That this is not a mere assumption can be shown in those cases in which the hereditary character appears only, or preeminently, in one sex as, e.g., color blindness which appears mostly in the male. If a color-blind individual is mated with an individual with normal color vision the heredity of color blindness in the next two generations corresponds quantitatively with what we must expect on the assumption that the chemical substances determining color vision are contained in the sex chromosomes. In the color-blind individual some-

thing is lacking which can be found in the individual with normal color perception. The factor for color vision is obvi-

THE MECHANISTIC CONCEPTION OF LIFE 23

ously transmitted through the sex chromosome. In the next generation color blindness cannot appear, since each fertilized

egg contains the factor for color perception. In the second generation, however, the theory demands that one-half of the males should be color blind. In man these conditions cannot be verified. T. H. Morgan has found in a fly (Drosophila) a number of similar sex-limited characters which behave like color blindness, e.g., lack of pigment in the eyes. These flies have normally red eyes. Morgan has observed a mutation with

white eyes, which occurs in the male. When he crossed a white-eyed with a red-eyed female all flies of the first generation were red-eyed, since all flies had the factor for pigment

in their sex-cells; in the second generation all females and exactly one-half of the males had red eyes, the other half of the males, however, white eyes, as the theory demands. From these and numerous similar breeding experiments of Correns, Doncaster, and especially of Morgan, we may conclude with certainty that the sex chromosomes are the bearers

of those hereditary characters which appear pre-eminently in one sex. We say pre-eminently, since theoretically we can predict cases in which color blindness or white eyes must appear also in the female. Breeding experiments have shown

that this theoretical prediction is justified. The riddle of Mendel’s law of segregation finds its solution through these experiments and incidentally also the problem of the determination of sex which is only a special case of the law of segregation, as Mendel already intimated. The main task which is left here for science to accomplish is the determination of the chemical substances in the chromosomes which are responsible for the hereditary transmission of a quality, and the determination of the mechanism by which these substances give rise to the hereditary character. Here the ground has already been broken. It is known that for the

formation of a certain black pigment the cooperation of a substance—tyrosin—and of a ferment of oxidation—tyrosinase

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THE MECHANISTIC CONCEPTION OF LIFE 25

—is required. The hereditary transmission of the black color through the male animal must occur by substances carried in the chromosome which determine the formation of tyrosin or tyrosinase or of both. We may, therefore, say that the solution

of the riddle of heredity has succeeded to the extent that all further development will take place purely in cytological and physico-chemical terms. While until twelve years ago the field of heredity was the stamping ground for the rhetorician and metaphysician it is today perhaps the most exact and rationalistic part of biology, where facts cannot only be predicted qualitatively, but also quantitatively. VII. THE HARMONIOUS CHARACTER OF THE ORGANISMS

It is not possible to prove in a short address that all life phenomena will yield to a physico-chemical analysis. We have

selected only the phenomena of fertilization and heredity, since these phenomena are specific for living organisms and without analogues in inanimate nature; and if we can convince

ourselves that these processes can be explained physicochemically we may safely expect the same of such processes for which there exist a-priori analogies in inanimate nature, as, e.g., for absorption and secretion. We must, however, settle a question which offers itself not only to the layman but also to every biologist, namely, how we shall conceive that wonderful “‘adaptation of each part to the whole” by which an organism becomes possible. In the answer to this question the metaphysician finds an opportunity to put above the purely chemical and physical processes something specific which is characteristic of life only: the “‘Zielstrebigkeit,” the “harmony” of the phenomena, or the “dominants’ of Reinke and similar things. With all due personal respect for the authors of such terms I am of the opinion that we are dealing here, as in all cases of

26 THE MECHANISTIC CONCEPTION OF LIFE

metaphysics, with a play on words. That a part is so constructed that it serves the “whole” is only an unclear expression for the fact that a species is only able to live—or to use Roux’s

expression—is only durable, if it is provided with the automatic mechanism for self-preservation and reproduction. If, for instance, warm-blooded animals should originate without a circulation they could not remain alive, and this is the reason why we never find such forms. The phenomena of “adaptation” cause only apparent difficulties since we rarely or never become aware of the numerous faultily constructed organisms which appear in nature. I will illustrate by a concrete example that the number of species which we observe is only an infinitely small fraction of those which can originate and possibly not rarely do originate, but which we never see since their organization does not allow them to continue to exist long. Moenkhaus found ten years ago that it is possible to fertilize the egg of each marine bony fish with the sperm of practically any other marine bony fish. His embryos apparently lived only a very

short time. This year I succeeded in keeping such hybrid embryos between distantly related bony fish alive for over a month. It is, therefore, clear that it is possible to cross practically any marine teleost with any other.

The number of teleosts at present in existence is about 10,000. If we accomplish all possible hybridizations 100,000,000 different crosses will result. Of these teleosts only a very small proportion, namely about one one-hundredth of 1 per cent, can

live. It turned out in my experiments that the heterogeneous hybrids between bony fishes formed eyes, brains, ears, fins, and pulsating hearts, blood and blood-vessels, but could live only a limited time because no blood circulation was established

—in spite of the fact that the heart beat for weeks—or that the circulation, if it was established at all, did not last long. What prevented these heterogeneous fish embryos from reaching the adult stage? The lack of the proper “dominants’’? Scarcely. I succeeded in producing the same type of faulty em-

THE MECHANISTIC CONCEPTION OF LIFE 27 bryos in the pure breeds of a bony fish (Fundulus heteroclitus) by raising the eggs in 50 c.c. of sea-water to which was added

2 c.c. 1/100 per cent NaCN. The latter substance retards the velocity of oxidations and I obtained embryos which were in all details identical with the embryos produced by crossing the eggs of the same fish with the sperm of remote teleosts,

e.g., Ctenolabrus or Menidia. These embryos, which lived about a month, showed the peculiarity of possessing a beating

heart and blood, but no circulation. This suggests the idea that heterogeneous embryos show a lack of “adaptation” and durability for the reason that in consequence of the chemical difference between heterogeneous sperm and egg the chemical processes in the fertilized egg are abnormal. The possibility of hybridization goes much farther than we have thus far assumed. We can cause the eggs of echinoderms to develop with the sperm of very distant forms, even mollusks and worms (Kupelwieser); but such hybridizations never lead to the formation of durable organisms.

It is, therefore, no exaggeration to state that the number of species existing today is only an infinitely small fraction of those which can and possibly occasionally do originate, but which escape our notice because they cannot live and repro-

duce. Only that limited fraction of species can exist which possesses no coarse disharmonies in its automatic mechanism

of preservation and reproduction. Disharmonies and faulty attempts in nature are the rule, the harmonically developed systems the rare exception. But since we only perceive the latter we gain the erroneous impression that the “adaptation of the parts to the plan of the whole” is a general and specific characteristic of animate nature, whereby the latter differs from inanimate nature. If the structure and the mechanism of the atoms were known to us we should probably also get an insight into a world of wonderful harmonies and apparent adaptations of the parts to the whole. But in this case we should quickly understand that

28 THE MECHANISTIC CONCEPTION OF LIFE the chemical elements are only the few durable systems among

a large number of possible but not durable combinations. Nobody doubts that the durable chemical elements are only the product of blind forces. There is no reason for conceiving otherwise the durable systems in living nature. VIII. THE CONTENTS OF LIFE

The contents of life from the cradle to the bier are wishes and hopes, efforts and struggles, and unfortunately also disappointments and suffering. And this inner life should be amenable to a physico-chemical analysis? In spite of the gulf which separates us today from such an aim I believe that it is attainable. As long as a life phenomenon has not yet found a physico-chemical explanation it usually appears inexplicable.

If the veil is once lifted we are always surprised that we did not guess from the first what was behind it. That in the case of our inner life a physico-chemical explanation is not beyond the realm of possibility is proved by the fact

that it is already possible for us to explain cases of simple manifestations of animal instinct and will on a physico-chemical basis; namely, the phenomena which I have discussed in former papers under the name of animal tropisms. As the most simple

example we may mention the tendency of certain animals to fly or creep to the light. We are dealing in this case with the manifestation of an instinct or impulse which the animals cannot resist. It appears as if this blind instinct which these animals must follow, although it may cost them their life, might be explained by the same law of Bunsen and Roscoe, which explains the photochemical effects in inanimate nature.

This law states that within wide limits the photochemical effect equals the product of the intensity of light into the duration of illumination. It is not possible to enter here into all the details of the reactions of these animals to light; we only wish

THE MECHANISTIC CONCEPTION OF LIFE 29 to point out in which way the light instinct of the animals may possibly be connected with the Bunsen-Roscoe law. The positively heliotropic animals—i.e., the animals which go instinctively to a source of light—have in their eyes (and occasionally also in their skin) photosensitive substances which undergo chemical alterations by light. The products formed in this process influence the contraction of the muscles—mostly indirectly, through the central nervous system. If the animal is illuminated on one side only, the mass of photochemical

reaction products formed on that side in the unit of time is greater than on the opposite side. Consequently the development of energy in the symmetrical muscles on both sides of the body becomes unequal. As soon as the difference in the masses

of the photochemical reaction products on both sides of the animal reaches a certain value, the animal, as soon as it moves,

is automatically forced to turn toward one side. As soon as it has turned so far that its plane of symmetry is in the direction of the rays, the symmetrical spots of its surface are struck by the light at the same angle and in this case the intensity of light and consequently the velocity of reaction of the photochemical processes on both sides of the animal become equal. There is no more reason for the animal to deviate from the motion in a straight line and the positively heliotropic animal will move in this line to the source of light. (It was assumed that in these experiments the animal is under the influence of only one source of light and positively heliotropic. )

In a series of experiments I have shown that the heliotropic reactions of animals are identical with the heliotropic reactions of plants. It was known that sessile heliotropic plants bend their stems to the source of light until the axis of sym-

metry of their tip is in the direction of the rays of light. I found the same phenomenon in sessile animals, e.g., certain hydroids and worms. Motile plant organs, e.g., the swarm spores of plants, move to the source of light (or if they are

30 THE MECHANISTIC CONCEPTION OF LIFE

negatively heliotropic away from it), and the same is observed in motile animals. In plants only the more refrangible rays from green to blue have these heliotropic effects, while the red and yellow rays are little or less effective; and the same is true for the heliotropic reactions of animals. It has been shown by Blaauw for the heliotropic curvatures of plants that the product of the intensity of a source of light

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