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NATIONAL ACADEMY OF SCIENCESBIOGRAPHICAL MEMOIRS

VOLUME XIII - FOURTH MEMOIR

B I O G R A P H I C A L M E M O I RO F

JACQUES LOEB18591924

B Y

W. J. V. OSTERHOUT

PRESENTED TO TH E ACADEMY AT THE ANN UAL MEETING, 19 30


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JACQUES LOEBOSTERHOUT

[Reprinted from the JACQUES LOE B MEMORIAL VOLUME, TH E JOURNAL OFGENERALPHYSIOLOGY, September 15, 1928, Vol. viii, No. 1, pp. ix-xcii.]

JACQUES LOEB.B Y W . J. V. OSTERHOUT.

If I venture to write of Jacques Loeb, it is not to create a portraitbut only to set forth facts to aid those who would follow in hisfootsteps. In this I bespeak the charity of the reader. And if thewriting achieve any part of its purpose it is because of many whoin loving veneration gave loyal aid.

Loeb's ancestors were among those illuminati who forsook Portugalon account of the intolerance of the Inquis ition: they settled at M ayenin the Rhine province several generations before he was born. Hisfather, Benedict Loeb, was an importer, aman of simple tastes, moreintereste d in science (especially in physics, m athem atics, and geology),in literature, and in collecting books than in business. He wasextremely reserved, and much of an aesthete. He married BarbaraIsay and their first child, Jacques, was born April 7, 1859, and wasfollowed by a second, Leo, some ten years later.The father's sympathies were strongly French and thus it cameabout that theeager mind of Jacques absorbed French as well asGerman culture, all the m ore because he lived in a region where F renchinfluence made itself strongly felt. His father, hatin g Prussianism ,looked longingly toward the democratic institutions ofFrance and ofthe United States.In 1873 the mother died and three years later the father followedher. Jacq ues, an orph an of 16, accepted a position in the bank of anuncle inBerlin. Shortly after, on the advice of an uncle, ProfessorHarry Bresslau, he entered theAskanische Gymnasium in Berlin.It was a purely classical school, with very little science, from whichhe graduated at the head of his class, with special mention forfluency in speaking La tin. At his dep artu re his teache rs gave him acopy of Zeller's "Philosophic der Griechen" with an inscriptioncautioning him not to become too liberal!

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NATIONAL ACADEMY BIOGRAPHICAL MEMOIRSVOL. XIII

His teachers took it for gran ted t ha t he would become a philosopherand with this in mind he entered the University of Berlin in 1880 andattend ed the lectures of the philosopher Paulse n. Bu t he soon con-cluded that metaphysical philosophy could not give satisfactoryanswers to the two questions uppermost in his mind: Is there such athing as free will? and, What are the instincts?He seems to have conceived a distaste for metaphysics at this timeand in his subsequent career the only philosopher who influenced himappears to have been Mach.The second semester of this academic year was spent at the Uni-versity of M uni ch: then , hoping to gain some light on the questionof the will, he went to Strassburg, entering th e labo ratory of G oltz whowas studying localization in the brain and endeavoring to refute thetheories of M unk and Hitzig. He re he remained five years and on th eadvice of Goltz took a medical degree in 1884 and the Staatsexamenin 1885. He then spent a year with Zuntz in Berlin where he con-tinued his work on brain physiology.

The results of his work were presented in a thesis entitled "DieSehstorungen nach Verletzung der Grosshirnrinde" (1, 2).1 Munkand Hitzig promptly denounced the paper and its author in no un-certain term s. There was nothing personal in this since it was merelya natural consequence of the rivalry between opposing schools at atime when bitt er polemics were only too common in Germ any. Neve r-theless it was a severe disappointment after five years of hard laborand it was a comfort to receive a letter from William James congratu-lating him upon his maiden- public ation: for this friendly act Loebdid not cease to be grateful and throughout his life he always seemedto be on the lookout to perform similar acts of kindness for youngscientists.He w as now fairly launched on th e scientific career which he p ursue dwith extraordinary success and which revealed mental powers of thehighest order. His restless mind mu st c ontinually find new ideas andnew enthusiasms as an outle t for its energies. He had a passionatelove of truth and what appeared to him to be true had to be so ex-pressed that all could feel the inspiration and see the beauty of what

1 The numbers refer to the numbers in the bibliography which appears in thisnumber of the Journal.31.9


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his keen hypotheses, often startling in their audacity and beauty,and attractive for their simplicity and clarity, aroused and stimulatedhis readers. Often his dreams were as inspiring as his actua ldiscoveries.N ot long after leaving Zuntz the direction of his future work beganto show itself. In the fall of 1886 he became assistant to Fick, pro-fessor of physiology at W iirzburg. He re the famous bota nist Sachsbecame his friend, even going so far as to invite him to go on hiswalks, a condescension most unus ual from an ordinarius to an ass istan t.And under the influence of Sachs his program commenced to assumemo re definite form. He had begun with the problem of the freedom ofth e will and his formulation of it was chara cteristic : if the will be freeit cannot be controlled; this question must be tested experimentally.At that time it was customary to attribute volition to lower animalsand it was natural to attack the problem there. The idea tha t be-havior might be controlled by operations on the brain led to hisexpe rimen ts with Goltz. Bu t these did not seem promising, and fora time he was uncertain.It was the privilege of Sachs to lead him in the right direction, forLoeb saw that if he could control animals as Sachs controlled plantsth e problem of the will could be attack ed scientifically. H e lost notime in setting to work: the results exceeded his fondest hopes andhenceforth the way was plain. H e went forward so rapidly th at intwo years he had published his first paper on the theory of animaltropisms that was to bring him fame.In the fall of 1888 he returned to Strassburg as assistant to Goltzand while here he did some work in collaboration with v . Ko ranyi ofBud apest (14 ). Th e winter of 1889-90 he spent in Nap les carrying onexperiments on heteromorphosis and the depth migrations of animals(in the latter work collaborating with Groom (16)): and it was herethat he became interested in America through his contact withHenry B. Ward and W. W. Norman.In the spring of 1890, at the home of Professor Justus Gaule (pro-fessor of physiology in Zurich and a former assista nt of Go ltz),he m eta young American, Miss Anne Leonard, who had just received herdocto rate in philology at the Un iversity of Zurich. Th e acq uaintanceresulted in an engagement and they were married in October of the

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same year. After the ma rriage, which took place in America, theyreturne d t o N aples for the w inter where he devoted himself to experi-ments on heteromorphosis since he was convinced that not only the"will" of the animal but also the form and function of its organs andits course of development m ight be controlled by the experimenter, anidea quite contrary to concepts then prevailing.At this time he was undecided whether he should continue to livefrugally on his patrimony and devote himself wholly to research oraccept an academic chair, which he dreaded because of its interfer-ence with his investigations. Bu t he deemed th at his new responsi-bilities ma de it imp erative to find a position. Feeling mo re and moreirritation at the military and political conditions in Germany, andhaving, like his father, a hatred of militarism, his thoughts turnedtoward America. Bu t there was no position in sight. At last he hadan inspiration: he would earn his living as an oculist, devoting partof his time to practice and the rest to research. He began to frequentthe clinic of his friend D r. F ick, in Zurich, bu t after six weeks gave upin despair, saying "I cannot live unless I continue my scientific work.These problems haun t me night and day and I must go on or perish ."While in this state of mind he received an offer of a position at BrynMawr College from Miss Thomas (then dean of Bryn Mawr) whichwas accepted with enthusiasm. He arrived in Bryn Maw r in Novem -ber, 1891, to assume his new duties, having been delayed owing to th earrival of his first-born child, Leonard.He was hap py to be in America and he enjoyed Bryn Maw r. Hehad a few graduate students, among whom was Miss Ida H. Hyde.But the facilities for his work were insufficient and in January, 1892,when Dr. Whitman asked him to join his staff at the new Universityof Chicago, he accepted. At the same time he agreed to give thecourse in physiology at Woods Hole during the following summer.At Woods Hole he was in his elemen t. He enjoyed giving thecourse: he was able to work without hindrance and he met a groupof men who shared his ideals and enthusiasm. He spent most of hissummers in Woods Hole during the remainder of his life, except forthe years spent at the University of California.On reaching Chicago in the autumn he found things in a state ofchaos. Th e W orld's.Fair was in prepa ration and only one university*

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building was completed. An apartm ent house had been leased for ayear to harbor the scientific departments of the university (one de-par tm ent to a floor). When the first qua rter opened there was nota piece of appa ratus in the building. In this, as in so ma ny othertrying circumstances, Loeb's sense of humor came to his aid: it wasone of his outstanding qualities and it is a great pity that this sketchcanno t, from its very natu re, dwell upon it. Bu t those who seek tounderstand his character should not underestimate this quality whichwas a wonderful help in a long and difficult strugg le, made dou blytrying by his supersensitive nature.

The following ten years in Chicago were busy and happy onesduring which he became a naturalized citizen and definitely tookroot in the Un ited Sta tes . An imp ortant circumstance linkinghim more firmly to his new environment was the birth of twochildren, Rob ert F . and A nne, which had the grea ter significancebecause of his intense devotion to dom estic life. Indeed his everymoment, apart from his laboratory, was spent with his family.

After a short time the department of physiology was separatedfrom th at of biology and Loeb was placed at its head; David J.Lingle and A. P. Mathews were associated with him in the depart-me nt. A physiological labor atory was dedicated in 1897. Amongthose who worked with him during this period (either at Chicagoor Woods Hole) were C. R. Bardeen, Elizabeth E. Bickford, 0. H.Brown, S. P. Budgett, Elizabeth Cooke, Martin H. Fischer, W. E.Carrey, W. J. Gies, A. W. Greeley, Irving Hardesty, W- H. Lewis,R. S. Lillie, E. P. Lyon, S. S. Maxwell, Anne Moore, C. H. Neilson,W. W. Norm an, R. Burton O pitz, W. H. P ackard, J. van Du yne,R. W. Webster, Jeanette C. Welch, and W. D. Zoethout.His work was at first largely concerned w ith tropisms and heteromor-phosis. He found th at these studies involved recent discoveries inchem istry and physics. He became deeply interested in the theory ofArrhenius and thus came to write the famous series of papers on thephysiological effects of ions. A direct o utgro wth of this was his dis-covery of artificial parthenogen esis and antago nistic s alt action in 1899.The winter of 1898-99 was spent in California at Pacific Grove,where he had expected to work on marine material but since he wasunable to carry out this plan he devoted his time to writing. The

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outcome was the "Comparative Physiology of the Brain and Com-parative Psychology" (62) written in German and translated by Mrs.Loeb. This was not an isolated instance of her aid for she con stantlycooperated with him in literary work.Loeb was greatly attracted by the genial climate and the possi-bility of working on marine material all the year around, and when acall to th e Unive rsity of California came in 1902 he accepted . Alaboratory was built for him at Pacific Grove not very far from thesite of the Jacques Loeb L aborato ry to be erected b y StanfordUn iversity. The Un iversity of California Publications in Physiologybegan in 1903; in October of the same year the ph ysiological labor a-tory at Berkeley was dedicated, the principal address being deliveredby Wilhelm Ostwald. In th e following year Arrhenius and de Vriesspent some time at the University of California to the great delightof Loeb who had becom e deeply interested in their work: this acquaint-ance ripened in to a firm friendship. This is equally true of th e latervisits of Boltzmann and Rutherford.Among those who worked with him a t this time were F. W. Bancroft,G. Bullot, T. C. Burn ett, G. C. Elder, M . H. Fischer, A. L. H agedoorn,W. 0. Redman King, E. v. Knaffl-Lenz, H. Kupelwieser, C. B. Lip-m an, J. B . Ma cCa llum, S. S. Maxwell, A. R. M oore, Wolfgang O stwald,T. B. Robertson, C. G. Rogers, Charles D. Snyder, R. Wulzen, andH. Wasteneys.In accepting the call to California Loeb had not realized how muchhe would be cut off from co ntact with his fellow scientis ts. He wasnaturally so averse to travel that he made no attempt to attend meet-ings of his colleagues in the East (and it was surprising that in1909 he attended the Darwin Centenary in Cambridge, England,went to the Vlth International Congress of Psychology in Geneva,the 350th Anniversary Celebration of the University of Geneva, the500th Annive rsary Celebration of th e University of Leipsic, and tothe XVIth International Congress of Medicine in Budapest, and in1911 atten ded the first Mo nist Congress in H am bu rg). This isola-

tion had much to do with his consideration of offers from Europe(especially from Budapest) and his final acceptance of a call to TheRockefeller In sti tut e for Medical Research in 1910. He desired tobe able to devote himself entirely to research and he w as deeply in ter-324


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ested in t he idea of carrying on w ork in general physiology in connec-tion with medicine. He thou ght th at in this way those engaged inmedical research might more easily see to what extent advance in theart of healing depends on our knowledge of the nature of the cell andhow medical progress may be quickened by such fundamental prin-ciples as general physiology can sup ply. (See in this connection th eletter reproduced on pages xvii-xix.)He found the atmosphere of the Ins titu te so congenial and stim ulat-ing th at his activity in research became greater than ever. He de-lighted in meeting other workers at the noon hour when all the stafflunched together and he inspired the younger men as few could do.In 1918 he founded the Jo urn al of General Physiology (in collabora-tion with the writer) and a series of Monographs on ExperimentalBiology (in collaboration with T. H. Morgan and the writer), both ofwhich met obvious needs.Among those who worked in his laboratory (either at the Instituteor at W oods Hole) were F . W. Bancroft, M . G. Banus, R. H. Beutner,McKeen Cattell, K. G. Dernby, W. F. Ewald, D. I. Hitchcock, K.v. Korosy, M. Kunitz, R. F . Loeb, Mrs. A. R. Moore, J. H . No rthrop,H . Wasteneys, and N . Wuest. I t should be added th at throughouthis connection with the Institute his labors were lightened by theefficiency and devotion of his secretary, Miss Nina Kobelt.His previous studies were continued for a time and late r there werenew developments, such as his investigations on bioelectrical phe-nomena and on qua ntita tive aspects of regeneration. He also took u panew the properties of proteins. It w as a subject th at ha d longattrac ted him : he had m ade a beginning years before b ut thereseemed then to be no guiding principles sufficiently well establishedto mak e it possible to proceed with assurance. Nevertheless theproblem was constantly in his mind and at length he discovered away to attac k it. In his earlier researches the dissociation theo ry ofArrhenius had furnished a clue and in the later work he found aguide in the Don nan principle. By applying this he was able to givequantitative explanations of some of the most important propertiesof colloids and to reduce them to simple mathem atical law s;

In the m idst of this imp ortant work he was persuaded to go to Ber-mu da for a brief holiday. A few day s later he was stricken w ithangina pectoris, and after a short illness his death occurred, on F ebru -32 5


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mental work.I wish to tell you how much I appreciate your kindness. A research

position is o f course my ideal; the question is whether or not the R. I. desiresto add a new department nam ely that of Experim ental Biology the latter ona physico-chemical instead of on a purely zoological basis. In my opinionexperimental biology the experimental biology of the cell will have to formthe bash n ot only of Physiology but also of General Pathology and Therapeutics.

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7 do o< /A/n/fe that the Medical Schools in this country are ready for the newdeparture; the experimental B iology in the Zoological departments willbe one sided and remain so. The only place in Am erica where such anew departure could be made for the cause o f Medicine would be theRockefeller Institute or an institution with sim ilar tendencies. Themedical Public a{ large does not yet fully see the bearing of the new scienceof Experim. Biol. {in the sense in which I understand it) on Med icine.

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ary 1 1, 1924. I t had alw ays been his desire to work up to the la stmom ent and to die in one of the places whose na tura l bea uty appealedto his ima gination . It seemed therefore in accordance with his wishtha t the end should come during a visit to Bermuda in the midst ofthe most active investigations of his life.His ashes were brought to Woods Hole for interm ent. A memorialtablet was placed in the Marine Biological Laboratory and in TheRockefeller In st itu te for M edical Research . It is bordered by theleaves of Bryophyllum, which had served for his experiments onregeneration but which he had not known in its wild state until inBermuda he had been delighted to see it everywhere bloomingprofusely.Enshrined within this border are the chief subjects to which hedevoted himself during a life tim e of unre m itting labor. All of themrepresen t fundam ental 'problems of biological research . Tho ugh atfirst sight they may seem to present no obvious continuity it would bea great mistake to suppose tha t it is absent. As with all great investi-gators, each new question arose natu rally out of the preceding. Therewas no runn ing after strange gods or foreign problem s. Th e task inhand demanded all his power of attention and it rewarded the seekerby continually unfolding new and promising leads to the very last.The end was not discernable at the start: nor did he dream whenbeginning with the freedom of the will that he would end by studyingcolloidal system s. Yet it was a tran sition as na tura l as the progressof Pasteur from crystals to microbes.

II .Loeb's work was too diversified and extensive to permit a completeaccount in the limits here prescribed. The most th at can be at-tempted is a general sketch of the evolution of his ideas, omitting alldetails save those which give definiteness to the picture.To understand the development of his thought we must go backagain to the sta rt. He began with the problem of the freedom of thewill and he felt that in experiment lay the only chance of progress.He turned, naturally enough, to the idea that behavior might becontrolled by operations on the bra in: for this reason he went to stud ywith Goltz. Here lie became acquainted w ith the experiments on

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dogs which had led Munk to think that the act of vision involves aprojection from the retina to a certain region of the cerebral cortexand that extirpation of certain parts of this region produces blindnessin corresponding part s of the retina. Loeb carefully repeated theseexperiments but was unable to confirm Munk.Many years afterward Henschen concluded from observations onhuman pathology that such a projection exists but not in the part ofthe cortex where Munk had located it and this idea was confirmed byMinkowski's experiments on dogs. . Loeb then took up the discussionfrom an entirely new angle. He called atte ntio n to the work of in-vestigators who had found that in the coloration of their skins certainfish reproduce a pattern, such as a checker board, forming the bottomof the aqua rium . Ex tirpatio n of the eyes or of the optic ganglia in thebrain or cutting the sympathetic nerve fibres which go to the pig-men ted cells of th e skin preve nts this phenom enon. Hence the pathis known and Loeb suggested th at what travels along this path may bean "im ag e" in the sense th at for each dark or bright point of the o bjectthere is a corresponding st ate of excitation first in the retina and subse-quently in the optic nerves and in their terminal ganglia in the brain.This illustrates wha t often happened in his work. Drop ping aproblem which did not seem to be leading anywhere he would never-theless keep it always in the back of his mind so that if new facts

turned up he could at once turn them to good use.Seeing the necessity for quantitative methods in dealing with thephysiology of the brain he devised a method of measuring the effectsof attention and m ental a ctivity by recording the pressure exerted b ythe hand upon a dynamometer while the subject was engaged In read-ing or ciphering (5). It w as found tha t these activities had a decidedeffect on the pressure imparted to the dynamometer.2 This ideaproved to be useful and suggestive.Later Loeb returned repeatedly to the physiology of the brain andin his book on the subject (62) made useful suggestions such as thosefound in his discussion of the sequence of reflexes proceeding from onesegmental reflex to another which he called "chain reflexes."His early work on the brain had failed to open the experimental

2 Cf. also Welch, J. C, Am. J. PhysioL, 1898, i, 283.330


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approach tha t he had hoped for. Bu t fortuna tely he soon afterwardcame under th e influence of Sachs who had clearly shown th at plan tsin their responses to light and certain other stimuli behave as simplemac hines. No t only the brilliant experiments of Sachs bu t his re-markable personality, his creative imagination, and broad philosophicviewpoint inspired Loeb, who was seized with a desire to test uponanimals the illuminating conceptions that Sachs ha.d formulated instudying plants.

Loeb's method of procedure is illustrated by his experiments onthe caterpillars of Porthesia which issue from their winter nests andclimb to the tips of the branches of trees w here the y find the openingbud s which serve them as food. It was supposed th a t the y foundthe right situation, in some cases before the food was actually ready,by a marvellous instinct. To explain th e origin and the hered ity ofsuch an instinct might seem to require very complicated hypotheses.But Loeb brushed all this aside by a few simple experiments show-ing th at these animals are slaves of the light. Th ey climb upw ardtoward the light until they reach the tips of the branches and therethey remain. They act like photochemical machines to such anextent that if food is placed behind them when they are starving theyare unable to turn their heads away from the light to take nourish-m ent. It seemed possible th at th is effect m ight be produced by aphotosensitive substance reacting more strongly on the illuminatedside and hence (through the medium of the nervous system) affectingunequally the symmetrical muscles on the two sides so as to turn thehead toward the light. To explain the heredity of such an "ins tinc t"we need only suppose that the parent transmits to the offspring theability to produce the photosensitive substance under the properconditions.

One must therefore cease to speak of the will of this animal andregard it as a matter of mechanism, completely under the control ofthe experimenter. "T he desire of the moth for the star" began toseem less mysterious.Thus at the very outset he came to the conclusion that certaininstincts may be resolved into tropisms and it soon became evidentthat no hard and fast line could be drawn between instinct and intelli-gence. In later work he developed these ideas. Finding th at th e

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addition of carbonic acid to water may produce in an aquatic animal,ordinarily indifferent to the light, a reaction drawing it irresistiblytoward a source of illumination, he raised the question whether thismay help us to put certain psychological problems upon a physico-chemical basis. If behavior may be changed by the addition of anacid why not by the secretions of a gland? Might not this idea beapplied to attraction between the sexes, which may involve a changefrom a selfish to an altruistic attitude? And why limit the considera-tion to glandular products? Since Pawlow and his pupils have pro-duced a salivary secretion in dogs by means of optical or auditorysignals it no longer appears strange that what we call an idea shouldbring about chemical changes in the body.

It is evident that these considerations may throw some light on thenature of ethics. Loeb put the matter as follows (214, page 31):"If our existence is based on the play of blind forces and only a matte r of chance;if we ourselves are only chemical mechanismshow can the re be anethics forus?The answer is, that our instincts are theroot of our ethics and that the instinctsare just ashereditary as is the form of our body. We eat, drink, and reproducenot because mankind has reached an agreement tha t this is desirable, but because,machine-like, we are compelled to do so. We are active, because we are compelledto beso byprocesses in ourcentral nervous system; and as long as human beingsare not economic slaves the instinct of successful work or of workmanship deter-mines the direction of their action. The mother loves andcares for herchildren,

not because metaphysicians had the idea that this was desirable, but because theinstinct of taking care of the young is inherited just as distinctly as the morpho-logical cha racters of the female body. We seek and enjoy the fellowship of humanbeings because hereditary conditions compel us to doso. We struggle for justiceand truth since we are instinctively compelled to see our fellow beings happy.Economic, social, and political conditions or ignorance and superstition may warpand inhibit the inherited instincts and thus create a civilization with a faulty orlow development of ethics. Individual muta nts may arise in which one or theother desirable instinct is lost, just as individual mutants without pigment mayarise in animals; and the offspring of such mutants may, if numerous enough,lower the ethical status of a community. Notonly is themechanistic conceptionof life compatible with ethics: itseems the only conception of life w hich can lead toan understanding of the source of ethics."He therefore regarded the study of tropisms as of fundamental

importance not only for biology but likewise for psychology and forphilosophy and he endeavored to place it upon a sound scientific basis.

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He tried to find quan titative relations and he was able to show in somecases that animals obey the Bunsen-Roscoe law which states thatequal amounts of energy in the form of light produce equal results{i.e. that for equal effects intensity multiplied by time of exposureequals a constant) as had already been shown for plants by Blaauw.The tropism theory would lead us to expect that when light comesfrom two different directions an animal will place itself so that theeyes will be equally illuminated on bo th sides. If the relative intensityof the lights be changed the animal should change its position accord-ingly. If in addition the animal obeys th e Bunsen-Roscoe law vary -ing the time of exposure to the light should have the same effect as aproportiona te change in the intensity . Ew ald, working in Loeb'slaboratory, found that the eye of Daphnia takes up a position inaccordance with this law. Loeb then showed in collaboration withEwald (240) and later with Wasteneys (291) that the heliotropiccurvature of the stems of the polyp Eudendrium obeys this law. Incollaboration with Northrop (300) he showed that the larvae of thebarnacle when exposed to two sources of light m ove at an angle whichagrees with this law: they also showed that when the horseshoe crabis tethered by a string attached to its tail and allowed to orient itselfbetween two sources of light the position it assumes is in accordancewith expectation (389). These results togethe r with those of otherobservers served to establish the principle on a firm basis.

As the result of Loeb's work the motions of animals came to beexplained more and more on the basis of tropisms rather than ofsingle reflexes: few movements exemplify simple reflexes and in manycases they represent groups of reflexes which are better described astropisms.The study of tropisms led him to question some current notionsregarding the function of the ce ntral nervous system. Th e flight ofth e mo th into th e flame, which had been rega rded as a typica l reflex, heexplained as a simple tropism like the turning of a plant to the light.In the case of the plant the mechanism consists of an apparatus forreceiving the stimulus and for transmitting it to the place where themotion takes place. He therefore asks, W hy is it necessary to assumeanything else in this animal: why postulate that the central nervoussystem does anything more tha n transmit the stimulus? And why333


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not explain othe r reflexes on the same basis? Th is would indic atethat the problem of coordinated movements needs a fresh attack andthat the cause of coordination may, in some cases at least, be foundoutside the central nervous system.It was a natural thing for him to pass on from the study of reflexesand tropisms to attack the problem of consciousness by seeking toresolve it into the simpler elements which compose it. He dennedconsciousness as the phenomena determined by associative memorythe presence of which can be experimentally determined by ascertain-ing whether the animal is capable of learning: where this is lackingconsciousness cann ot exist. Th e fundam ental problem of psychologyis the mechanism of associative memory and the manner in whichstimuli are transmitted; the method of attack is to try to discoverwha t properties of colloids ma ke such phenom ena possible. For thesolution of these problems we mu st use the metho ds of physical chem-istry, particularly as employed in the study of protoplasm.

Many of these views are summarized in his "Comparative Physi-ology of the Brain and Comparative Psychology" (62) which had astrong influence, at a time when it was much needed, in replacinganthropomorphic speculation by sound experiment.It may be added that although his attention was chiefly devoted toheliotropism where he could work quantitatively, he fully realized theimportance of the other tropisms on which he made so ma ny imp ortan tobserva tions. He pointed out very clearly the fundamen tal signifi-cance of tropism s in the struggle for existence, their im portanc e inrelation to adaptation, and their role in developmental mechanics.His writings gave an enormous impetus to the experimental study ofanimal behavior and encouraged the expectation that it might bebrought under the control of the experimenter and his suggestionsinfluenced both psychology and philosophy.For him nothing was mpre natural than to go further and inquire:If we can control the behavior of the anim al why not seek to d eterm inealso its form and developm ent? This led to his experimen ts in thefield which he called physiological morphology. He found it possibleto control regeneration so that, for example, certain hydroids can bemade to produce "roots" in place of "stems," just as botanists hadpreviously found for pla nts. This he called heterom orphosis.

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He accepted the explanation given by the botanists (and especiallyby Sachs) that the organs are determined by "organ-forming mate-rials" so that where these materials collect the appropriate organs willbe formed.The impression made by these studies is well rendered by Herbst(whose opinion derives especial weight from his critical scientificatt i tude).

"Wirkten sie doch wie ein heller Sonnenstrahl, der plotzlich in das Dunkel derMorphologie fiel, die damals ganz im Banne phylogenetischer Forschung stand,welche wegen ihrer nicht zu beseitigenden Unsicherheit, ja mitunter Willkur, unsjiingere Forscher nicht mehr befriedigen kon nte. Hier aber schienen einem Ta t-sachen gegeben zu sein, die in einem die Hoffnung erweckten, derraaleinst auchdas tierische Gestaltungsgeschehen kontrollieren zu konnen. Freilich um dieEntwicklung des Organismus aus dem E i handelte es sich in diesen Arbeiten nich t,sondern nur um die Regeneration verlorengegangener Teile und um ahnliche Er-scheinungen. Die Wirkung dieser Schriften war so gross, dass man sie nur mitderjenigen der Arbeiten von Trembley, Bonnet und Spallanzani auf Forscherund Laien der zweiten Halfte des 18. Jah rhunderts vergleichen kann , dennwie damals die erste Hochflut in der Erforschung der Regenerationserscheinungeneinsetzte, sowalzte sich nach dem Erscheinen der Be itrage Loebs die zweite heran,befruchtend und reichen Ertrag erbringend fur die biologische Wissenschaft."3

He later produced such monstrosities as Siamese twins, triplets,or quadruplets in the egg of the sea urchin by diluting the sea waterand causing the egg to burst and extrude one or more rounded massesof protoplasm . On replacing the egg in ordinary sea wate r eachextruded portion gave rise to an embryo, as did also the main body ofthe egg to which it was attached, the attachment persisting as theembryos developed.By such experiments he hoped to analyze the forces which controldevelopment, believing that the biologist should aim at as completecontrol of living matter as the physicist and chemist have over theirmaterial, and that the best hope of success lay in applying theirme thods to biology. He ma de brilliant use of this conception. Hebecame especially interested in the dissociation theory and as one ofthe first results he published the well known series of papers on thephysiological effects of ions. He tho ught th a t the specific effects of

3 Herbst, C , Die Naturwissensckqften, 1924, xii, 400.335


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salts on the organism might be due to the combination of ions withsubstances in the protoplasm whose properties might thereby bealtered . H e found an analogy in the case of soaps where potassiummake s a soft soap, sodium a hard er one, calcium one tha t is still harde r,and so on (63).To test these ideas he exposed organisms to salts in varying concen-trati on s. Fertilized eggs placed in sea water whose osmotic pressurehad been increased by the addition of sodium chloride could not seg-ment but if replaced in ordinary sea water after two hours they passedrapidly into a many-celled stage. His explanation was th at in themore concentrated solution the nucleus divides but the cytoplasm isunable to do so; on replacing the eggs in ordinary sea water the divi-sion of the cytoplasm follows at once. Fou r years later Norm an re-peated this work, adding magnesium chloride to the sea wa ter. Stilllate r Mo rgan ma de similar experiments on unfertilized eggs and foundon replacing them in ordinary sea water th at they began to segment b utthis soon stopped and no larvae were formed. About th e same timeMead observed that the addition of a little potassium chloride to thesea water caused the unfertilized eggs of the m arine worm Chxtopterusto expel their polar bodies.4Loeb found in 1899 (68, 69) that unfertilized eggs of the sea urchinwhich had remained for two hours in a mixture of equal volumes ofsea water and tw o and a half m olar magnesium chloride would develop

into plutei when replaced in ordinary sea water. Th e announce men tof this fact was received by his scientific colleagues with a degree ofincredulity which bordered almost on indignation and there was ageneral feeling th at his results must be due to contam ination by sperm,which are widely dispersed throughou t the sea water du ring the spawn-4 Prior to all of these observations was that of O. and R. Hertwig (1887) thateggs treated with strychnine occasionally segment a few times. Still earlier Greeff(1876) had observed that parthenogenesis sometimes occurs in the starfish Astera-canthion (the development did not proceed beyond the blastula stage) and O.Hertwig (1890) had confirmed this for Asterias and Astropeden bu t neither of theseauthors had determined the conditions under which this rare phenomenon tookplace. It was also known tha t eggs of arthropods , echinoderms, and annelidsmight begin to segment after lying for some hours in sea water. There also existin the litera ture other reports of the beginning of cleavage under various conditions(122, pages 83 and 84, also 157).

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ing season. There was, however, a difference in the app earance ofeggs which were fertilized by sperm and those which were caused todevelop by th e trea tme nt with magnesium chloride since in the latterth e fertilization mem brane is not as eviden t as in the former (indeedit was supposed for a long time t ha t the la tte r ha d no mem brane atall). Doubt presently disappeared and throughout the civilized worldwent a stir such as a scientific announcement seldom makes.It was soon found that the action of magnesium chloride consistedmerely in raising the osmotic pressure and that equally good resultscould be obtained by the addition of other neutral salts or even ofsugar, as well as by the use of sea water concentrated by evapora-tion. This was therefore known as the osmotic me thod of artificialparthenogenesis.Loeb stated that the importance of this discovery consisted intransferring the problem of fertilization from the domain of mor-phology to that of physical chemistry and he undertook to discoverwha t physical and chemical changes cause the egg to develop. H efirst tried to imitate the formation of the typical fertilization mem-bran e which is produced by the entrance of the sperm. H e succeededin this by exposing the eggs to certain fatty acids and then replacingthem in sea water, but the development was not normal unless thistreatment was followed by exposure to sea water of increased osmotic

pressure or to sea water deprived of oxygen or containing a littlepotassium cyanide. In this case the plutei often appeared p erfectlynorm al. La ter Delage succeeded in carrying larvae produced by arti-ficial parthenogen esis to the- stage of sexual m atu rity . It ma y beadded that Loeb, using the method of Guyer and of Bataillon, laterproduced parthenogenetic frogs and raised them to sexual maturity(277, 354).It is of interest to note th at the sea urchins raised by D elage weremales. Th e frogs raised by Loeb were of both sexes: the chromosomenumber was regarded by Goldschmidt as diploid and this was later

confirmed by Parmenter.5

Two questions presented themselves, What are the physical andchemical changes which produce the fertilization membrane, and,5 Parmenter, C. L., / . Gen. Physiol., 1925-28, viii, 1.

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W hy is the after-treatm ent necessary? To answer the first he soughtto discover whether other means could cause the formation of thetypical mem brane. It was produced by certain cytolytic agents,particularly those which markedly affect surface tension, such assaponin, bile salts, and soap. It could also be produced by lipoidsolvents, such as benzene and toluene (as Herbst and Hertwig hadalready observed), by alcohols and ethers, by certain bases, by ultra-violet light, and by other means. These agents are destruc tive andkill the egg unless it be removed in time and given an appropriateafter-treatment.

Loeb concluded th at all of these agents act on a substance , proba blya lipoid, at the surface of the protoplasm causing certain colloids toswell and thereby lift up a delicate membrane from the surface (thequestion whether this membrane is preformed or is produced duringthe treatm ent is not essential). This could be broug ht abou t, forexample, if the protoplasm at the surface consisted of an emulsion,the inner phase consisting of particles surrounded by a film of lipoidwhich might be removed by solution or precipitation or even bymechanical agitation so as to bring the particles into direct contactwith the outer phase and cause them to swell and to lift up the fer-tilization membrane.The question arose, How can an alteration of the surface of the seaurchin egg cause development? Perha ps by its effect on oxidation:W arburg had state d th at oxidations occur chiefly at th e surface, hencea change in the condition of the catalysts at the surface or an increaseof permeability might increase oxidation.When the membrane is formed in artificial parthenogenesis of thesea urchin there is a great increase in oxidation (as Warburg found)and the egg quickly dies if there is no additional tre atm en t. Bu t ifoxidation is suppressed for a time (by depriving the eggs of oxygen orby adding a trace of potassium cyanide to the sea water) they liveand can afterward develop normally. Tem porary suppression ofoxidation is evidently not the sole factor involved, since increasedosmotic pressure is even more effective and certain narcotics act inmuch the same way without diminishing oxidation. All of theseagents stop development for a time and this would seem to be theessential thing: during this period the egg has a chance to recover

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from the effects of the treatment which produces the membrane andif the suppression does not last too long normal segmentation occurswhen the egg is replaced in ordinary sea water.His general conclusion was that the sperm brings to the egg twosubstances, one of which a cts on th e surface of the protoplasm in sucha way as to form a fertilization membrane, the other factor having acorrective action which prevents any harmful results"of the processesimmediately following membrane formation.Evidence in favor of this idea was obtained on placing unfertilizedeggs of certain species of sea urchin in h ype ralka line sea wate r andadding starfish sperm. The results seemed to indicate tha t the spermbears at its surface a substance which can cause membrane formationby mere contact with the egg but that the substance bearing the

corrective factor lies deeper in the sperm and produces no effect unlessthe sperm actually pen etrates the egg. At any rate many caseswere found in which the sperm produced mem brane formation bu t t heeggs did not develop unless treated with hypertonie sea water and itwas assumed that in these cases the sperm did not penetrate butmerely induced membrane formation by coming in contact with th esurface of the egg and that the membrane thus formed prevented thesperm from pe netratin g. In other cases where the egg went on devel-oping it was assumed that the sperm had penetrated.With some species of sea urchins it was possible to produce mem-

brane formation with an aqueous extract of starfish sperm which hadbeen killed by heating to 60C. Such eggs behave like those trea tedwith a fatty acid and it is necessary to give them the after-treatmentwith hypertonie sea water to make them develop normally, as wasalso the case if such eggs are subjected to t he action of living sperm ofthe shark or the rooster which do not penetrate but only give to theegg the substance which causes mem brane formation. If this sub-stance were like the so called lysins of blood it would seem possibleto produce membrane formation with the blood of various foreignspecies. This proved to be the case with the blood of ox, sheep,pig, and rabb it, and certain inve rtebrate s. In some cases it was neces-sary to sensitize the eggs by preliminary treatment with strontium orbarium . In all cases the eggs perish unless given the after-treatm ent.

Lysins of the sea urchin have no effect on eggs of the same species,339


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jus t as the lysins of sheep's blood can not affect th e corpuscles of sheepthough th ey quickly destroy those of other anima ls. Is this becausethe lysins cannot penetrate cells of their own species or because anti-bodies protect the cells even if th e lysins penetr ate them ? Loeb'sanswer was tha t if the egg of the sea urchin contained an antibod y th esperm could not produce a mem brane and it therefore seemed probablethat the immunity of blood corpuscles to their own lysins may be dueto the fact that the lysins cannot penetrate.Other possible explanations have been suggested for many of thephenomena of artificial parthenogenesis, but those given here seemedto him on the whole the most probable. La ter work brought to lightnew facts, as, for example, th at the corrective trea tm ent could precedeas well as follow the treatment which produced the membrane, butthese did not essentially change his viewpoint.W ha t has been said relates especially to the sea urchin. Otherforms show divergencies: for example, in the starfish egg fertilizationproduces no increase in oxidation and othe r differences exist. Buthis main conceptions were developed from the experiments with seaurchin eggs and it has therefore seemed better to confine the accountchiefly to these.This brief outline of his method of analyzing the problem of fertili-zation says nothing of the many disappointments, the frequent fail-ures, the long and tedious groping in the dark which preceded success.Nor does it touch on the w ealth of new problems th at came with eachdiscovery. An example is seen in the experim ents in which sea urchineggs were treat ed w ith the sperm of the starfish. Und er ordinaryconditions no result is obtained but Loeb discovered that if the seawater were made slightly more alkaline fertilization took place and anormal development followed.He found that fertilization could be brought about by the spermof ophiurans, holothurians, or even of molluscs. Bu t the employmentof such foreign sperm did not affect the character of the larva; whichhad the same appearance as if fertilization had been effected by seaurchin sperm of the same species.Since development could be so easily started the question arosewhether it could also be stopped and reversed at the will of the experi-mente r. Th e question of reversib ility of develop ment ha d first been

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raised by Loeb in 1900 (75, 78) when he observed the transformationof a hydroid polyp into the less differentiated material of the stolonwhich can in turn give rise to a new polyp. Since that tim e a numberof instances of reversibility have been described by other observers.He found that the artificial parthenogenesis of the sea urchin egginduced by alkali was reversible. Eggs trea ted with the alkalinesolution followed by a hypertonic solution would develop in sea waterbut if, after removal from the hypertonic solution, they were placedfor a short time in sea water containing sodium cyanide or chloralhyd rate they would not develop when replaced in sea water b ut actedas if no treatm ent h ad been given them (237, 239, 264). The initia-tion of development by bu tyric acid also proved to be reversible.Another suggestion arising from the study of the developing eggconcerns th e mech anics of gro wth . D urin g th e first period of divisionthe nuclear material of the egg increases in a manner which indicatesthat cytoplasmic materials are transformed into nuclear substance.Nuclear division may occur at fairly regular intervals and at eachdivision the nuclear m ater ial is app roxim ately doubled. It followsth at the m ass of nuclear materia l produced at each division is propor-tional to the mass already present which might mean that the reac-tion which produces nuclear m aterial is catalyzed by some con stituentof the nucleus so that the greater the amount of nuclear materialalready on hand the more rapid the rate of the reaction. This, as hepointed out, is the case with an autocatalytic reaction (125, 139,168). This suggested to T. B. R obertson the possibility th at thegrow th of the entire organism might agree with the curve of au toc ata -lysis and an examination of the av ailable da ta convinced him th at thiswas the case. About the same time Wolfgang Ostwald reached th esame conclusion.The experiments on artificial parthenogenesis called his attentionto the problem of na tura l de ath . This interested him profoundly,par tly because of its bearing on ethical problems. Is death a necessaryconsequence of the process of growth and development, or is it some-thin g superimposed, capab le of being postpon ed or eliminated? Heexpressed his views as follows:

"The writer showed in 1902 that the problem of fertilization is intimately con-nected w ith the problem of the prolongation of the life of the egg cell. The unfer-34 1


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tilized mature egg dies in a comparatively short time, which may vary from a fewhours to a few weeks according to the species or the conditions under which theegg lives. The fertilized egg, however, lives indefinitely, inasmuch as it gives rise,not only to a new individual, bu t, theoretically at least, to an endless series of genera-tions. The death of the unfertilized egg is possibly the only clear case of naturaldeath of a cell, i.e., of death which is not caused by external injuries, and the act offertilization is thus far the only known means by which the na tura l dea th of a cellcan be preven ted. The two problems, fertilization and prolongation of life, arethus interwoven, and th e experiments on the mechanism of fertilization become atthe same time studies on the problem of natural death and prolongation of the lifeof the egg cel l." (157, English edition, page 1.)

He pointed out that while the fertilization of the egg by sperm ofthe same species prolongs the life of the egg indefinitely its span oflife may be very brief if the sperm of certain other species is employed.He found that the sensitiveness of the sea urchin to the effect ofabnormal solutions increased as development proceeded so that whencertain unfavorable solutions are improved by the addition of seawater the eggs die more quickly because they rapidly develop to astage in which they are much more sensitive than before (245).The discovery of artificial parthenogenesis made it possible toanalyze the factors which prolong the life of the egg. Th e usualtreatment of the sea urchin egg consists in first causing membraneformation in the unfertilized egg but eggs so treated die much morequickly tha n untrea ted eggs. It m ight therefore seem th at the"corrective treatment" usually applied after membrane formation isresponsible for prolonging the life of the egg. Bu t when the correc-tive treatment is applied before membrane formation the eggs liveno longer than untreated eggs: if the membrane formation is sub-sequen tly induced the y live and develop. Hence it would app ear asif both treatments are needed.Membrane formation in the sea urchin egg appears to be followedby deleterious processes and only if the development of the egg betemporarily suppressed by the "corrective treatment" can it live.Under these circumstances we arrive at the paradoxical result thatthe life of the egg may be prolonged by the temporary application ofpotassium cyanide or by depriving it of oxygen or by subjecting it tothe action of narcotics.

Another method of attack ing the problem of death was by studying342


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tem pera ture coefficients. He believed th at this me thod had greatimpo rtance for biology and w orkers in his laboratory had been pioneersin applying it to such life phenomena as the heart beat (Snyder,Robertson) and to nervous conduction (Maxwell, Snyder).Experiments on the sea urchin egg (made at high temperatures)showed that lowering the temperature 1C. doubled the length of lifealthough it had been shown by the work of other investigators (withwhich his own agreed) that at lower temperatures it was necessary toraise the temperature 10C. to double the speed of development.This might be regarded as an indication that development and deathare not due to the same chemical processes for in that case no suchdifference in the effect of temperature would exist and this might ex-plain the extraordinary richness of life in the colder parts of the oceanwhere the low temperature would have a much greater effect in pro-longing the life of the developed organism than in retarding develop-ment.

But the question assumed a different aspect when experimentswere made on vinegar flies (in collaboration with No rthr op ). The yare so short-lived that the experiments can be carried on withoutraising the temperature to an abnormal level so that the normalduration of life is studied rather than the rate of killing by abnor-mally high temp eratu re. The y worked with vinegar flies free frommicroorganisms so that there could be no suspicion that death wasbrought about, as Metchnikoff had suggested, by toxic substancesproduced in the intestinal tract by the action of bacteria.The experiments showed that the effect of temperature was practi-cally the same on development and on length of life and this was in-terpreted to mean that the duration of life depends on the time re-quired to complete a chemical reac tion (or series of reac tion s). Th enature of this reaction could not be denned but many of the cells ofthe body when removed from the influence of the rest can go ondividing indefinitely as shown by Leo Loeb, Harrison, and others,and especially by the experiments of Carrel. This is also true ofcancer cells, as shown by Leo L oeb. Such cells are potentially im-mortal like the unicellular organism.

Closely ^connected with the se subjects is th at of oxidatio n whichearly occupied his attention and led him to suggest that the nucleus343


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is the center of oxidation in the cell. La ter Wa rburg concluded t ha toxidation is largely confined to the surface of the sea urchin egg butthe experiments of Loeb and Wasteneys did not confirm this view.They also made experiments on the effect of narcotics on the seaurchin egg and came to the conclusion that, contrary to the theory ofVerworn, certain substances can produce narcosis with little or nodiminution in the rate of oxidation.

Important as these problems were Loeb did not allow himself to bediverted from his basic program, out of which had sprung the experi-me nts on artificial partheno genesis. This program dealt with thefundame ntal prope rties of protoplasm as affected b y ions. In orderto ascertain the effects of individual ions it is desirable to employ anorganism which can live either in distilled water or in fairly concen-tra ted salt solutions. This is the case with the fish Fundulus whoseeggs develop equ ally well in distilled water or sea wa ter. Loeb wassurprised to find that on adding to distilled water as much sodiumchloride as is contained in sea water the eggs could not develop, inother words the sodium chloride is toxic and it was evident that theother salts found in sea water must somehow overcome this toxicity.The announcement of this fact was received with genuine astonish-ment.

He found that the addition of all sorts of salts with bivalent ortrivale nt cations in the right prop ortions could more or less completelyremove the toxicity due to salts with monovalent cations. He spokeof this as antagonistic salt action and he called solutions such as seawater, in which the toxicity is suppressed by the admixture of salts inthe proper propo rtions, a physiologically balanced solution. Inorder to have antagonistic salt action toxic salts must be present insufficient concentration to produce injurious effects and these in-jurious effects must be overcome by other salts which have a protec-tive action.Bo tanists had long before found th at pla nts (which can live for sometime in distilled water) grow much bette r when certain salts are added.Very often such salts have only a nutritive function since there areno toxic effects to be overcome because the solutions are too dilute(just as Fundulus requires no addition of protective salts in a solutionof sodium chloride having a concentration of 0.125 M or less). W hen

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H erbst found t ha t all the s alts of sea water w ere needed to raise marineanimals he worked from th e same viewpoint. There was nothin g tosuggest that sodium chloride was toxic because his animals died veryquickly in distilled wa ter. B ut in th e case of Fundulus eggs Loebshowed th at the tox icity of sodium chloride could be largely overcomeby adding salts without nutritive value; some, indeed, were verytoxic when used alone, such as the salts of lead and zinc: it was evi-dent that the action of such salts must be purely protective.

The striking fact that monovalent cations are antagonized bybivalent and still more by trivalent cations led Loeb to suggest thatthe sign and valence of the ion may in many cases be far more im-portant than its chemical nature, as had already been found to be thecase in certain experiments on colloids. This suggestion proved to bea highly stimulating one.Ringer had found long before this that when the heart of a frog isperfused with a solution of sodium chloride the beats grad ually dimin-ish and ultimately cease: the addition of either calcium or potassiummakes possible a resumption of activity but the beats are not normalunless both calcium and potassium are added in the proper propor-tions. Ringer concluded th a t there exists between calcium andpotassium an antagonism analogous to that which exists betweencertain poisons of the heart, for example between atropine and mus-carin e: but for R inger sodium chloride was an indifferent substa ncewhereas Loeb regarded it as toxic. It may be added tha t OscarLoew had shown that the toxicity of magnesium for certain plantslargely disappe ars if sufficient calcium is adde d. But these wo rkersarrived at no such far-reaching conclusions as Loeb. The experim entson Fundulus opened up a new point of view: had not this been thecase the y could not have created so much interest. In this connec-tion we may quote the remarks of Hober:

"Loeb fand, dass das Ca nicht bloss durch die chemisch verwandten Mg, Srund Ba ersetzt werden kann, sondern auch durch die Protoplasmagifte Ni, Mn,Zn, Pb , Cr u.a. Dies war ein so une thorte r Befund, dass im Hinblick daraufein so ausgezeichneter Kenner der Salzwirkungen wie Overton damals den Satzschrieb: 'Dass die Calciumsalze durch Bariumsalze cder die Salze der zweiwerti-gen Schwermetalle in keiner Weise ersetzt werden konnen, musste jedem toxi-kologisch gebildeten Physiologen von vornherein klar sein.' Heute haben wir

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eine Reihe von Beweisen dafiir, dass in der Tatmehr oder weniger gutdiezwei- und dreifach positiv elektrisch geladenen Ionen einander vertreten konnen,und obwohl Loeb, wie gesagt, ausseiner Entdeckung mit weitreichendem Blicksofort die Konsequenz auf die KoUoidchemie zog, so hat diese doch erst in neues terZeit, in unmittelbarer Anknupfung an die physiologischen Vorbilder, besondersdurch Studien von Freundlich, das richtige Nachbild schaffen konnen; es gibtanorganische Kolloidsysteme, die das physiologische Kolloidsystem recht getreuimitieren. Loebs Entdec kung war der wichtigste Anstoss, das Interesse an demStudium der physiologischen Bedeutung der Salze neu zu beleben undzi'gleichdurch rein theoretische Untersuchungen zu vertiefen, und wieviel das besagen will,das leh rt ein Blick in die physiologische, pharmakologische und klinische Lite raturunserer Tage. Sie stro tzt von Untersuchungen iiber Ionenwirkungen; um kleins-ten Schwankungen in den Normalkonzentrationen der Ionen nachgehen zu konnen,wurden vorziigliche Mikromethodenersonnen; die Wirksamkeit der normalerweiseanwesenden Kationen, besonders der mehrwertigen Ca und Mg, wurde von denverschiedensten Seiten beleuchtet, ihr Verhaltnis zu den Protoplasmakolloiden,insbesondere zum Eiweiss, und ihrVerhaltnis zu den Ionen des Wassers vielseitigdurchforscht, wobei auch wichtige klinische Interessen und das Interesse am Aus-bau der Theorie ihrer Wirkungen gewichtig mitsprachen; die Erforschung derbioelektrischen Phanomene trat in ein neues Stadium ein. Bei diesem ganzenNeubau hatLoeb selber anden verschiedensten Stellen mitgewirkt."6

When an organism can live in distilled water the question of an-tagonism is perfectly clear, but when this is not the case there may bedifficulty in distinguishing between the nutrient and the protectiveeffects of salts. Fundulus in its early stages develops as well in dis-tilled water as in sea water but this cannot continue indefinitely since,for example, calcium is necessary for the formation of bones. WhenFundulus develops in sea water the function of calcium may be purelyprotective at the start; later it becomes nutritive also.

But notwithstanding the complications due to nutritive functions,the importance of the* protective action of salts is clearly evident insuch solutions as sea water. This is also true of the blood of mammalsand in this connection Loeb experimented on muscles, finding forexample that in the absence of calcium they undergo rhythmicalcontractions, and he suggested that this might account for tetanyunder certain conditions. This suggestion has since found practicalapplication in medicine.

The important question arose, What is the mechanism of the pro-6 HSber, R., Klin.Wmk., 1924, iii, 511.

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tectiv e action of salts? Loeb found tha t as soon as the embryoescaped from the egg membrane the whole picture changed and it wasno longer possible, for example, to diminish the toxicity of sodiumchloride by the addition of salts of lead or of zinc. Nor did calciumalone suffice to remove toxicity since the addition of potassium wasalso necessary (282).

He therefore concluded that the membrane plays an importantr61e and that in a balanced solution the salts probably acted on it(or perhaps on the micropyle, which is regarded as especially perme-able) in such fashion as to make it less permeable than in a solutioncontaining a single salt. Hence it would appear necessary th at thesalts should act simultaneously in protective action: this is not thecase with nutrient action where the salts can be given in succession.The recent work of Bodine7 and of Armstrong8 indicating thatdissecting off the membrane makes no essential change in certainreactions of the embryo, appears to mean that the seat of action isin these cases at the surface of the embryo.

Loeb also found that when eggs are placed in sufficiently concen-tra ted sea water the y float for several day s. In a solution of puresodium chloride they quickly sink and since he regarded the egg asnormally almost impermeable to water he believed that this resultindicated tha t salt had entered. Add ition of a small am ount of cal-cium chloride to th e solution of sodium chloride enabled the m t o floatfor days, indicating that it inhibited the entrance of salt.But it is also possible to assume that in certain cases penetrationoccurs and th at the antagonistic action takes place in the protoplasm,especially in those cases where acids are antagonized by salts and theexperiments show that the acid is absorbed by'the organism (270).

He also considered the possibility that certain salts penetrate morerapidly because they attach themselves to the surface so as to form amore concentrated layer which increases the concentration gradient.If some of the salt in this layer is displaced by an other s alt th e e ntran ceof the first salt will be somewhat inhibited (and its exit facilitated)producing an antagonistic effect (266). In this connection he ma de

7 Bodine, J. H., Proc. Nat. Acad. Sc, 1927, xiii, 698; Biol. Bull, 1928, liv, 396.8 Armstrong, P. B., / . Gen. PhysioL, 1927-28, xi, 515.347


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some very striking experiments with the dye neutral red: Funduluseggs stain more rapidly in distilled water than in solutions containingsalt or acid and lose the dye more rapidly in solutions containing saltor acid (without dye) than in distilled water.

The question of permeability began to assume an increasing im-portance as a factor which controls all the activities of the cell, butit was evident that for satisfactory progress methods must be foundof determining exactly how fast substances can pen etrate . He triedto test the hypothesis of Overton that the surface of the cell is lipoidand allows only substance s soluble in lipoid to ente r the cell. Th isseemed improbable because water passes rapidly into the cell and thesubstances normally taken up by the cell are in general insoluble inlipoid but are soluble in wate r. It seemed to him more probable th atthe surface of the cell is a protein film, such as forms spontaneouslyon the surfaces of aqueous solutions of prote in. At the same time hethought that lipoids are present in or close to the surface of the eggand that they play an important role in the formation of the fertiliza-tion membrane.

Since as a rule salts are alm ost or q uite insoluble in lipoid the y couldnot be expected to pe ne trat e a lipoid film, unless very slowly. Bu tLoeb found evidence for the penetration of salts: for example, afterthe heart has begun to beat in the embryo of Fundulus (while stillenclosed in the egg mem brane) it can be brought to a standstill by thepen etrati on of potass ium salts. It was found (266, 269, 286, 287,288, 289) th at the memb rane was almost impermeable to potassiumsalts in very dilute solutions but that the addition of more potassiumsalt (or certain other salts) made it more permeable: he called this"t he general salt effect." If too much salt was added it again becameimpermeable (antagonistic effect).

He pointed out the analogy to globulins which are insoluble in lowconcentrations of salts, become soluble when the concentration in-creases sufficiently, but again become insoluble when the concentra-tion becomes too great. He was therefore inclined to think th at th eincrease of permeability was due to the solubility of a constituent ofthe me mb rane which behaves like globulin. On this basis one migh texpect that the addition of a neutral salt would increase the diffusionof alkali into the egg (and augment its toxicity) but would' have the

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opposite effect on the diffusion of acid since analogous effects areobserved on the solubility of globulins (303). Th e experiment showedthat this expectation was justified.Loeb found th at to a certain extent t he behavior of potassium inentering the cell is paralleled by tha t of acids (270). He observedthat weak acids and bases appear to penetrate much more rapidlythan strong ones, indicating that the protoplasm is not readily per-meable to ions.As part of his studies on the physiological effects of ions he desiredto take up bioelectrical effects but his distrust of all but the simplestapparatus led him to postpone it until the advent of Beutner, whosetraining fitted him especially for the task . Together they studiedthe very interesting phenomenon of the "concentration effect," that

is, the potential difference observed in leading off from two placesin conta ct with different conc entration s of the same salt. Em ployin gmostly such plant tissues as apples and leaves of the India rubbertree they found that in dilute solutions they obtained the maximumvalues which were theoretica lly to be expected. The results indicatedthat the organism acts as a reversible electrode for all sorts of cationsbut the effects due to protoplasm are difficult to separate fromthose due to the dead cell wall.Somewhat similar results had previously been obtained by Mac-Donald but their theoretical significance had not been understood andthe work had been largely overlooked.Loeb and Beutner endeavored to find non-living models whichwould act similarly and this undertaking (subsequently continued byBeutner) led to the discovery that many organic substances immisciblewith water not only give the concentration effect but also act some-wh at like living tissue when brou gh t in con tact with a series of differentsalts of the same conce ntration (chem ical effect). Th us the way wasopened up for the study of bioelectrical phenomena on a new basis.As an illustration of his courage in attacking difficult problems we

may consider his treatm ent of organization and adaptatio n. He wasled to this problem by his experiments on the development of the egg.His general attitude may be stated in his own words:"It is generally admitted that the individual physiological processes, such asdigestion, metabolism, the production of heat or of electricity, are of a purely

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physicochemical character; and it is also conceded that the functions of individualorgans, such as the eye or the ear, are to be analysed from the viewpoint of thephysicist. When, however, the biologist is confronted with the fact tha t in theorganism the p arts are so adapted to each other as to give rise to a harmoniouswhole; and tha t t he organisms are endowed with stru ctures and ins tincts calculatedto prolong their life and perpetu ate the ir race, doubts as to th e adequacy of a purelyphysicochemical viewpoint in biology may arise. The difficulties besetting thebiologist in this problem have been rather increased than diminished by the dis-covery of Mendelian heredity, according to which each character is transmittedindependently of any other character. Since the number of Mendelian charactersin each organism is large, the possibility must be faced th at the organism is m erelya mosaic of independent hereditary ch aracters. If this be the case the questionarises: Wha t moulds these independent cha racters into a harmonious whole?"The vitalist settles this question by assuming the existence of a pre-establisheddesign for each organism and of a guiding 'force' or 'principle' which directs theworking out of this design. Such assumptions remove the problem of accountingfor the harmonious character of the organism from thefieldof physics or chemistry.The theory of natural selection invokes neither design nor purpose, but it is in-complete since it disregards the physicochemical constitution of living matte r a boutwhich little was known until recently." (290, pages v-vi.)

The question therefore is, What ensures the integrity of the or-ganism? He suggested th at th e un ity of the organism might belargely determined at the outset by the structure of the protoplasm.In some eggs a definite structure is indicated by regions differingin app eara nce : from each of these certain organs arise. In the secases the egg might be regarded as a rough model of the future em-bryo. The harmonious correlation of the parts of the embryo mighttherefore be determined by the arrangement of the parts of the egg.

The fact that the structure of the egg is important might possiblybe related t o the fact t h at t he size of the egg cann ot be artificiallydiminished beyond a certain point without interfering with develop-ment. He unde rtook ex periments like those performed on infusoria byNus sbaum and, employing different m ethods , caused th e egg of t hesea urchin to break up into small fragments. He concluded th atonly those fragments develop into plutei which contain in addition t othe nucleus a sufficient amount of certain constituents of the cyto-plasm.

Loeb felt that those who thought it impossible to account for de-velopment on a physicochemical basis might have been misled by the350


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assumption that the cytoplasm of the egg is more homogeneous thanis actually th e case. H e believed th at proper recognition of the im-portance of the structure of the egg might change this point of view.There are other things to consider, such as the mutual influence ofthe various parts, a factor which is capable in many cases of a mecha-nistic explanation. Th us he observed th at in the yolk sac of Fundulusthe pigment cells have at first no definite arrangement "but that theygradually are compelled to creep entirely on the blood vessels andform a sheath around them with the result that the yolk sac assumesa tiger-like m arki ng." He regarded this as a tropistic reaction andbelieved that such reactions play an important part in development.An analysis of the mechanics of development must include a studyof regeneration. It had been assumed by some th at when a missingpart of the organism is replaced there must be a directive force whichensures that the regenerated part shall be just what is needed tocomplete th e organism and enable it to perform its functions. Loebfound m any cases where this is not so ; for example, under some condi-tions a hydroid instead of regenerating a lost stolon produces a polyp"so that we have an animal terminating at both ends of its body in ahe ad ." Such cases of heteromorph osis are difficult to explain on thebasis of a directive force which operates to supply the needs of theanim al. The y become more intelligible if we assume th at th e forma-tion of organs is due to specific substances (as had been postulated bySachs and others in the case of plants) and th at where these substancesaccum ulate the organ in question will be formed. This accum ulationcan be controlled to a certain-exten t by th e experimenter. Loeb dis-cussed this in connection with such cases as the development of legsin tadp oles. Young tadpoles hav e no legs bu t the mesenchym e cellsfrom which th e legs are to develop are present a t an early stage. Or-dinarily no growth occurs during a long period (from four months to ayear or more) but Gudernatsch found that legs can be made to groweven in very young specimens by feeding them the thyroid glands ofvarious anima ls. Th e mechanism of thi s process is not clear butLoeb suggested (257) that the stimulation of the growth of body cellsmight be analogous to the process by which the egg is caused todevelop, i.e. by changes at the surface of the cell.Another way in which onepart can influence another is illustrated in

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plants: it seemed clear from the work of previous experimenters, aswell as from his own, that one part can inhibit another by divertingthe flow of formative ma terial. Thu s a bud at th e top of the stemtakes the material away from one lower down but if the terminal budbe removed the . othe r begins to deve lop.

These facts made him feel that a mechanistic approach to theproblem was possible. He went on to examine the equally impo rtantquestion of ada ptatio n. He showed th at m any characteristics of theorganism which are regarded as adaptive may be explained on amech anistic basis. Th e reaction s of animals to light depend on aphotochemical substance which m ay arise with out reference toadap tation and occ ur in anim als which pass their lives in tota ldarkness in the mud or under the bark of trees. One is no moreunder the logical necessity of supposing that heliotropism can ariseonly in response to a need or under the guidance of a "directive force"than in the case of galvanotropism where no one would dream of in-voking such conceptions . Th e reactions of a galva notropic animalare as beautifully developed as any tropism although in nature suchanim als are never exposed to electric cur rents . Since a mechanisticexplanation appears possible here why not in the case of other tro-pisms?

He emphasized the fact th at m any cases of "a dap tatio n" may verywell be the "preadaptations" of Cu6not, i.e. "adaptat ions" whicharise before they can be of any use, which would seem to rule out adirective force. Thu s many m arine organisms die when placed inconcentrated sea water but the fish Fundulus is an excep tion. If aportion of the ocean became landlocked so that the concentration ofsalts increased and all the fish except Fundulus died an observer m ighteasily suppose that these fish had gradually become adapted to themore concentrated sea water.

Curiously enough his atte m pts to increase the natu ral resistance ofFundulus by placing it in sea water which gradually became concen-trated by evaporation had little result.He stressed the fact that in many other instances, includingthe famous case of blind fish in caves, there is evidence in favor ofthe idea that the supposed "adaptation" may have been a "pre-adaptat ion."

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When adaptation really exists it appears in many cases as if it couldbe explained on a mechanistic basis without invoking a directiveforce, as, for example, when (in collaboration with Wasteneys) hebrought about an adaptation of Fundulus to life at higher tempera-tures, a change which has many physicochemical analogues.

These examp les may suffice to illust rate his poin t of view. He felt,however, that here as elsewhere quantitative experiments are anecessity and he therefore determined to undertake such experimentsin studyin g regeneration. H e proposed to ascertain whe ther in thisfield, long a stronghold of vitalism, careful measurements would revealthe rule of mechanism or the reverse.Obliged to put the problem aside until he could discover suitable

material he eventually found what he needed in the life plant ofBermuda (Bryophyllum calycinum). Its large leaves have numerousmarg inal indentatio ns in'which new pla nts arise when a leaf is sepa-rate d from the stem and placed in a moist atmosp here. He madenum erous experiments with this pla nt. He employed as a criterionof growth the dry weights of the par ts studied. Th e result was notdoubtful; w henever measurem ents could be mad e a machine-likeregularity became apparent; for example, not only did two leavesdetached from th e same point on the stem produce the same dry weightof new buds a nd roots, but when a leaf was removed, a small piece of t hestem being left attached to it, and the new growth was confined to theattached piece of stem, it was equal to the growth of new buds androots on a similar leaf dep rived of stem. He began a program ofresearch on this basis but the work progressed slowly because a singleexperiment might require weeks and he would not have more goingon than he could observe with minute care. Hence it happened th atat the time of his death the program w as only begun. He had, how-ever, arrived at some tentative conclusions which, even when theywere not novel, were of interest on account of their quantitative basis.

He concluded that the production of buds at one end of the stemand roots at the other was not due to differences in the "ascending"and "descending" materials, as Sachs and others had supposed; alsothat the formative material moves more readily toward organs wherethe most rapid growth occurs, which explains why those organs in-hibit others which are growing more slowly; also that gravity may

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rause sap to sink and so prom ote growth on the lower side. He like-wise concluded that no "wound hormone" exists.It is characteristic that he should so courageously attempt to placethis difficult subject on a quantitative basis and to formulate it inmathematical terms.An important episode which throws light on his habits of thought ishis work upon the prope rties of prote ins. His studies on the effectsof ions had resulted in a series of articles in which he developed theidea (simultaneously with Pauli) that ions combine with proteins toform ion-protein compound s (70, 308). He also ma de the suggestionthat pepsin owes its activity to its ionic state and that it is a weakbase which becomes more ionized in acid solution and hence moreactive (trypsin being considered a weak acid). Th e idea ha d beenpublished before, thou gh witho ut Loe b's knowledge. Th e suggestionwas stimulating and led others to investigate the subject with theresult that pepsin later came to be regarded as an amphoteric elec-trolyte (Michaelis) or as a monovalent anion (Northrop), trypsinbeing a monovalent cation (Northrop).Carrying his studies on proteins as far as he thought that existingmethods could give clear-cut results he turned aside to pursue certainother problems growing directly out of his work on ions, such as arti-ficial parthenogenesis and antagonistic salt action.But the fact that he laid them aside did not mean that they wereout of mind. For nearly twe nty years they remained in the back-ground awaiting the opportunity which only a new method couldfurnish. One day , washing some eggs of Fundulus on a filter to freethem from adhering salt solution, the idea occurred to him that hemight treat proteins in the same way to get rid of the excess of sub-stances which did not combine with them. He thereupon placedpowdered gelatin in solutions of acids and bases, rinsed off the excessof solution on a filter, and determined how much remained in thegelatin, his preliminary assumption being that this represented the

amou nt in actua l combination with the.prote in. Thu s a way seemedto be opened to determine whether proteins combined with thesesubstances in definite proportions. Although he subsequently aban -doned this method the fact remains that this idea was the startingpoint of his renewed activity in this field of work.354


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His experiments soon convinced him that the subject had falleninto confusion because of insufficient attention to the hydrogen ionconcen tration: methods of measuring and of controlling this had beendeveloped since he had first attacked the subject and he now madegood use of them, availing himself at the start of the assistance ofDr. K. G. Dernby. He had now found the needed clue and he setto work with characteristic energy.

The importance of the hydrogen ion concentration lies in the factthat in alkaline solutions the protein acts like an anion but in suffi-ciently acid solutions it behav es as a cation. At a certain hy drogenionconcentration (the isoelectric point) these two actions are approxi-ma tely equal. He found tha t gelatin at its isoelectric point (pH 4.7)is almost inert. It s combining power is so small th at it can easilybe freed from salts by bringing it to this point (a matter which cer-tain indus tries later foifnd to be of great prac tical im por tanc e). Atthis point its osmotic pressure, viscosity, power of swelling, and someother properties are at a minimum . On addition of acid or alkalithese properties increase and by plotting them against the pH valuescharacteristic curves are obtained.

The explanation of these curves came about in a very natural way.In order to measure the osmotic pressure of the solutions they wereplaced in bags of collodion, impermeable to gelatin but permeable towa ter and to salts . Th is created the condition necessary for a Do n-nan equilibrium and it became necessary to study the principle setforth by Donnan, particularly as previously applied by Procter andWilson to the swelling of prote ins. It w as found tha t by means ofthe Donnan principle all these curves received a quantitative ex-planation: this was so complete that Loeb felt justified in sayingthat until an equally satisfactory theory could be found his explana-tion seemed bound to stand.

The Donnan principle (more properly called the Gibbs-Donnanprinciple) states that ions inside a membrane which are unable topass thro ugh it* affect the be havior of those th at do, acting as if the yattra cted those of opposite sign (thereb y increasing their concentrationinside the membrane) and repelled those of the same sign (thus de-creasing their concentration inside). It m ay be expressed by th eequation:C- A{ = Co A

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in which C< and A { represent the concentrations inside the membraneof the cation and the anion respectively of a diffusible salt: C andA, are the corresponding concentrations outside.

The fact that the Donnan principle applies indicates that the pro-tein is present as ions (or charged particles acting as ions). At th eisoelectric point the numb er of ions is at a minimum . When t hesolution is made more alkaline they increase in number just as if theprotein were a weak acid: they also increase if acid is -added insteadof alkali, as if the protein were a weak base. Th e gelatin thereforeacts as an amphoteric electrolyte, behaving as a cation below pH 4.7and as an anion above this poin t. Assuming for convenience tha tthe molecule has one acid and one basic group we should have a t theisoelectric point NH 2 - R - COOH . On the addition of NaOHthis w ould beha ve like a weak acid such as acetic acid and give sodiumgelatinate, NH 2 - R - C O O " + N a+ (which m ay be wr itten G~ -f-Na+) . Bu t if HC1 were added th e gelatin w ould behave like a weakbase such as amm onia, giving gelatin chloride, Cl~ + NH 3+ R COOH (which m ay be written Cl~ + G+).

It is therefore clear that the behavior of gelatin depends on itsdegree of ionization. Th e properties mentioned above have a mini-mum value at the isoelectric point because the ionization is at a mini-mum, and these values increase when acid or alkali is added becausethe ionization increases.The Donnan principle leads us to expect that when protein is placedin a collodion sack which is permeable to water and to ordinary saltsbut not to the protein there will be a difference of potential betweenthe inside and outside of the membrane (mem brane poten tial). Noone had succeeded in finding this but Loeb was able to demonstratethat it is present and that its magnitude is in accordance with thetheory.These facts are in harmpny with the idea of Procter and Wilsonthat in the swelling of a gel each particle of protein acts very muchlike a collodion sac

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