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THE CELL AND PROTOPLASM

Publication of the American Association

for the Advancement of Science

No. 14

Publication Committee

C. V. Taylor, Chairman

Alva R. Davis

J. Murray Luck

C. B. VAN NiEL

Albert Tyler

Edited by Forest Ray Moulton

Published for the American Association for the Advancement of Science Smithsonian Institution Building, "Washington, D. C, by

The Science Press

1940

Copyright, 1940, by

THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE

THE SCIENCE PRESS PRINTING COMPANY LANCASTER, PENNSYLVANIA

FOREWORD

This volume on The Cell and Protoplasm is the tenth symposium published by the American Association for the Advance- ment of Science in the three years that have elapsed since it began such publications in 1938. Like the earlier volumes in this series, this one is a systematic and authoritative treatment by eminent specialists of an im- portant field of science.

In a sense the Cell Theory is not new, for the long history of its development in- cludes dim foreshadowings by Greek nat- uralists of Aristotle's time and approaches to it by Robert Hooke in 1665, nearly two centuries in advance of the important papers of Schleiden and Schwann, in com- memoration of the centennial of which this symposium was organized. In another sense the Cell Theory is always new, for every discovery respecting this primary and es- sential unit of living organisms, both plant and animal, has raised more questions than it has answered and has always widened the fields of inquiry.

The fact that there are many possible approaches to an understanding of the nature of the living cell is indicated by the variety of chief scientific interests of the seventeen contributors to this symposium. In biographical directories five of them are classed as zoologists, four as chemists, three as botanists, two as anatomists, and one each as a biologist, a geneticist and a bio- chemist. Specialists in seven fairly dis- tinct branches of science have participated in a survey of what has been established regarding living cells and protoplasm, often indicating what is only probable or con- jectural and sometimes pointing out what is quite unknown.

From the Table of Contents it will be found that this volume contains discussions of such various biological entities as cell walls, chromosomes, genes, viruses, en- zymes, hormones and vitamins; and of such various questions of mutual relation- ships as nucleus and cytoplasm, chromo- somes and genes, cell differentiation and external environment, cell differentiation and internal environment, and the cell and the organism. It will be found that there are reports on such various basic investiga- tions as the bridge between the living and

the lifeless, the biochemistry of micro-organ- isms, the physical and chemical properties of protoplasm and colloids, and the nature and mode of action of structural units in cellular physiology. Finally, illustrations will be found of the use of such technical means as the compound microscope and a discussion of the micromanipulation of living cells.

Previous symposia published by the As- sociation were presented at its meetings. This one was held during five days imme- diately following the meeting of the Pacific Division at Stanford University in June, 1939. It was not, however, local in its or- ganization nor participated in only by local scientists. Of the seventeen contributors, seven were from the Pacific Slope, one from the Middle West, six from the East and three from Europe. Thus to the variety of chief interests of the participants is added the wide diversity of their environment and immediate scientific associations.

It would be difficult to name a more im- portant and interesting subject for a joint discussion by biologists, biochemists and chemists than that treated in this sympo- sium, for protoplasm is the material basis of life and the cell is the fundamental unit involved in the vital processes of all the myriads of kinds of living organisms that inhabit the earth. The fact that this unit is common not only to all species of plants and animals but also to all their parts enormously multiplies the opportuni- ties for investigating its properties and the modes of its functioning. Its universal presence implies its importance in all prob- lems of growth, maturity and senescence, of health and disease, of heredity and vari- ation.

As its name indicates, the primary pur- pose of the Association is to contribute to the advancement of science. It is fulfilling this purpose in various ways, one of which is by publishing the best of the symposia that are presented at its meetings. In mak- ing available in this volume a clear, com- prehensive and documented summary of what is now known concerning living cells and protoplasm the Association makes a substantial contribution to progress in biology. F. R. Moulton

LIST OF CONTRIBUTORS

Irvino W. Bailey, M.F., Sc.D.

Professor of Plant Anatomy, Harvard University, Cambridge, Mass.

J. D. Bernal, M.A.

University Professor of Physics, Birkbeck College, University of London, London, England.

Robert Chambers, M.A., Ph.D.

Department of Biology, New York University, New York, N. Y.

C. M. Child, M.S., Ph.D., Sc.D.

Emeritus Professor of Zoology, The University of

Chicago, Chicago, 111.; Stanford

University, Calif.

Edwin G. Conklin, A.M., Ph.D., Sc.D., LL.D.

Emeritus Professor of Biology, Princeton Univer- sity, Princeton, N. J. ; Executive Vice-presi- dent, American Philosophical Society, Philadelphia, Pa.

Richard B. Goldschmidt, Ph.D., M.D., Sc.D.

Professor of Zoology, University of California, Berkeley, Calif.

Ross G. Harrison, Ph.D., M.D., Sc.D.

Osborn Zoological Laboratory, Yale University,

New Haven, Conn.; Chairman of the

National Research Council,

Washington, D. C.

L. V. Heilbrunn, Ph.D.

Associate Professor of Zoology, University of Pennsylvania, Philadelphia, Pa.

H. S. Jennings, Sc.D., Ph.D., LL.D.

Professor Emeritus, Johns Hopkins University, Baltimore, Md. ; Research Associate, De- partment of Zoology, University of California, Los Angeles, Calif.

Charles A. Kofoid, A.M., Ph.D., Sc.D., LL.D.

Emeritus Professor of Zoology, University of Cali- fornia, Berkeley, Calif.

0. L. Sponsler, A.M., Ph.D.

Professor of Botany, University of California, Los Angeles, Calif.

W. M. Stanley, M.S., Ph.D., Sc.D.

Member, The Rockefeller Institute for Medical Research, Princeton, N. J.

Albert Szent-Gyorgyi, M.D., Ph.D.

Professor of Medical and Organic Chemistry, De- partment of Medical Chemistry, University of Szeged, Szeged, Hungary

C. V. Taylor, A.M., Ph.D.

Herzstein Professor of Biology, Stanford Univer- sity, Calif.

Hugo Theorell

Director, Biochemical Division, The Nobel Insti- tute for Medicine, Stockholm, Sweden

C. B. VAN NiEL, Chem.E., D.Sc.

Professor of Microbiology, Hopkins Marine Sta- tion of Stanford University, Pacific Grove, Calif.

F. W. Went, M.S., Ph.D.

Professor of Plant Physiology, California Insti- tute of Technology, Pasadena, Calif.

TABLE OF CONTENTS

The Cell and Protoplasm. C. V. Taylor 1

Cell and Protoplasm Concepts : Histor- ical Account. Edwin G. Conklin 6

The Micromanipulation of Living Cells. Robert Chambers 20

The Walls of Plant Cells. Irving W. Bailey

31

Chromosomes and Cytoplasm in Pro- tozoa. H. S. Jennings 44

Chromosomes and Genes. Richard

B. GOLDSCHMIDT 56

Cellular Differentiation and External Environment. C. M. Child 67

Cellular Differentiation and Internal Environment. Ross G. Harrison 77

Cell and Organism. Charles A. Kofoid 98

The Biochemistry of Micro-organisms; an Approach to General and Com- parative Biochemistry. C. B. van NiEL 106

The Structure of Viruses. W. M. Stanley 120

Structure and Function of Some En- zymes. Hugo Theorell 136

Plant Hormones. F. W. Went 147

Vitamins. Albert Szent-Gyorgi 159

Molecular Structure in Protoplasm.

0. L. Sponsler 166

Protoplasm and Colloids. L. V.

Heilbrunn 188

Structural Units in Cellular Physiol- ogy. J. D. Bernal 199

7347^

THE CELL AND PROTOPLASM

By C. V. TAYLOR

SCHOOL OF BIOLOGICAL SCIENCES, STANFORD UNIVERSITY, CALIF.

The sixteen papers comprised in this volume were presented in a Symposium on The Cell and Protoplasm at Stanford Uni- versity, June 30-July 5, 1939. The occa- sion commemorated the one hundred years of advancement in knowledge of the proto- plasmic unit of living things after Schlei- den and Schwann's formulation of the Cell Theory.

The participants were men of merited eminence, including several distinguished biologists whose names have been familiar in biological science for more than a quar- ter of a century, along with others whose more recent analyses of the cell and its constituents have greatly extended the con- fines of biological knowledge and have doubtless pointed the w^ay for further stud- ies of fundamental importance.

The first three papers have to do pri- marily with early and modern concepts of the cell and protoplasm. The initial article by Professor Conklin on "An Historical Account of Cell and Protoplasm Concepts" reviews the results of investigations on the cell previous to the work of Schleiden and Schwann. The accurate descriptive ac- counts of these earlier investigators have evidently not been adequately recognized. Thus the degree of credit commonly ac- corded Schleiden and Schwann appears to be unwarranted because their accounts were antedated many years by the pub- lished findings of various, even superior, workers beginning notably with Robert Hooke (1665). This well illustrates the social nature of scientific discovery and rightly emphasizes that the end results of the successive achievements of many minds may come to have rather exclusive, and so undue, recognition.

The second paper, by Professor Cham- bers, on "The Micromanipulation of Liv- ing Cells," helps to resolve our modern

concepts of these living protoplasmic units to the essential nature and properties of their molecular constitution. As can be strikingly illustrated by motion pictures, the protein constituents of the protoplasm tend to retain their inherent state in the presence of an engulfed droplet of oil. Upon cytolysis, however, as induced through mechanical rupture of the nucleus or otherwise, a protein "skin" forms and becomes wrinkled around the droplet, much as also happens when such a droplet is added to a protein solution on a micro- scope slide. This unique behavior of the protein constituents of the protoplasm would seem to indicate a coherent property of proteins in the living cell which may be irreversibly changed if the characteristic structure of its protoplasm is disrupted.

Another modern aspect of the cell and protoplasm, gained chiefly from studies on protoplasmic elaborations, is presented in Professor Bailey's article on "The Walls of Plant Cells." The structural pattern of the cellulose wall laid down by the proto- plast evidently should offer invaluable clues to the nature and interaction of the protoplasmic constituents. Thus, the regu- larity of a specific pattern whether con- centric, radial, ramifying, or radiocentrie of a given cell wall would seem to reflect a predisposed regularity in the arrange- ments and orientations of constituents at the interface where the cell wall is derived. All evidence thus far indicates that the cellulose matrix of the cell walls of higher plants is a continuous, rather than a dis- continuous, system of anastomosed chain- molecules whose long axis is oriented par- allel to the long axis of the cellulose fibril. They exhibit positive anisotropy and sharply defined extinction angles in mono- chromatic polarized light. At present, there is no reliable evidence that the struc-

THE CELL AND PROTOPLASM

tural framework of the cell wall is ever composed of any randomly oriented chain- molecules.

Complementing these three papers on ''The Cell and Protoplasm" are the two that follow on "The Cell and Chromo- somes." The first of these is by Jennings on "Chromosomes and Cytoplasm in Pro- tozoa" and the second by Goldschmidt on "Genes and Chromosomes."

The well-known nuclear cycle that recurs with each cell division during the ontogeny of a multicellular organism is cited by Jennings as crucial evidence of material exchanges between the nucleus and the cytoplasm. Accordingly, each condensed chromosome enlarges during the later phases of mitosis to become vesicular, from material taken up from the cytoplasm. Within the resulting contiguous chromo- some vesicles which constitute the reformed nucleus, the newly acquired cytoplasmic material is altered and, as such, is returned again to the surrounding cytoplasm upon the subsequent breakdown of the vesicular wall of each chromosome, whose residue again condenses for the following mitosis. These cyclic interchanges and transforma- tions apparently provide the essential mechanisms of cellular differentiations both in the ontogeny of multicellular or- ganisms and in the racial variations of unicellular organisms. As illustrative of the latter, De Garis' recent results from crossing large and small races of Parame- cium are discussed. These results show that the ex-con jugants having unlike cyto- plasms but like nuclei retain their size dif- ferences for about 22 generations, where- upon these differences gradually disappear. Evidently, therefore, the two different cy- toplasms are finally transformed by the like nuclei so that the two races of unequal size come to have the same size.

By what mechanism of the nucleus the cyclic modifications, and so racial differ- ences, may be effected is discussed in the succeeding paper by Goldschmidt. His thesis tends to discount the commonly ac- cepted gene theory of Mendelian heredity and proposes instead a chromosome theory in which the occurrence of genes as discrete

entities, arranged bead-like in a definite order, need not be assumed. From the similarities in chromosome form and struc- ture in the cells of all organisms, wherein a visible fibril-like core may represent a single protein unit of definite stoichiomet- ric properties along its axis, it would be more in accord with recent X-ray, chem- ical, and polarimetric analyses to identify the chromosome as a chemical unit. Such a unit might show any amount of differ- ential chemical complexity in different chain molecules of similar length. This concept would ascribe to the chromosome a linear pattern and would account for mu- tational changes (the Bar-effect, mosaicism, position-effect, etc.) as due to changes in the chromosomal pattern (inversions, translocations, duplication of parts, etc.) rather than to changes within discrete par- ticles, or genes, of molecular order.

The demonstrable interrelations between cytoplasm and nucleus which would ac- count for differentiation in both the indi- vidual and the race obviously represent but one of the two major components in the fundamental phenomena of living things. The other essential component is, of course, the environment. The role of environmen- tal factors is well exemplified in the three papers that follow on developmental as- pects of the cell and its relation to the or- ganism. These include "Cellular Differ- entiation and External Environment" by Child, "Cellular Differentiation and Inter- nal Environment" by Harrison, and "Cell and Organism" by Kofoid.

The external environment of the primor- dial cell, according to Child, is a determin- ing factor in its differentiation at the very onset of develcpment. The cell's primor- dial pattern is essentially a surface-interior pattern which reflects an intimate relation- ship with its environment. Also, by action of a suitable differential in its external en- vironment, its polar or axiate differentia- tion is duly determined. Any one or more of various environmental differentials may induce this superimposed axiate pattern, as demonstrated in numerous experiments by Child and by others. Accordingly, the axiate pattern arises as a gradient which is

THE CELL AND PROTOPLASM

initially quantitative in nature and which, once established, constitutes a gradient in rate of metabolic activity. Moreover, this environmentally induced axial or meta- bolic gradient then subtends the produc- tion and transfer of active constituents (chemical substances) in differentiating cells and so predetermines the course of later development.

Factors of differentiation in later stages of early development are discussed by Har- rison as factors of the internal environ- ment. These are illustrated especially from his extensive transplantation experiments on amphibian larvae. Here the develop- mental pattern, which has progressed well beyond the initial axiate stage of Child's account, has demonstrably a primary cellu- lar locus (organizer) in the region of the dorsal lip of the blastopore, and later, vari- ous secondary loci, which determine organ differentiation throughout ensuing devel- opment. Depending upon the age of donor and of host as well as on the piece removed and its disposition where transplanted, the fate of the transplant and its effect upon the organogeny of the host are strikingly illustrated. From this it seems evident that the fate and effect of a developing part are functions of its relation to other parts. This fundamental relationship ob- viously marks the internal environment of cellular differentiation.

In the succeeding paper presented by Kofoid, it is emphasized, however, that even were the roles of both genetic and en- vironmental factors of ontogenetic devel- opment well understood, that knowledge, essential as it must be, could constitute only part of any adequate understanding of the cell and organism. For the organ- ism, beginning its individuality as a pri- mordial cell, represents in its complete life history not only the ontogeny that follows its unicellular stage but also the phylogeny preceding that stage. And all organisms exhibit in this fundamental respect com- parable life histories which may include, even for numerous so-called unicellular forms, a multicellular as well as a unicellu- lar phase. Accordingly, it is only in terms of their total life history as an expression

of their evolutionary, developmental, and environmental history that the cellular or- ganization of living things can have basic significance and the results of fundamental investigations a satisfactory basis of inter- pretation.

The two papers that follow, one on ''Chemical Aspects of Microorganisms" by van Niel, and the other on "The Structure of Viruses" by Stanley, mark a transition from consideration of the cell and proto- plasm of the more conspicuously cellular organisms to a discussion of the subcellular bacteria and of those ultramicroscopic, re- producing entities, the viruses, whose sys- tematic status, whether animate or inani- mate, apparently remains a problem of great moment.

Recognizing Schwann's important con- tribution not only to the formulation of the Cell Theory but also to the concept of yeast cells as vital agents of alcoholic fermenta- tion, van Niel recounts the later develop- ments of that concept, beginning especially with Pasteur, which have now led to a dis- tinctly basic and far-reaching generaliza- tion. This generalization affirms that all chemical activities of living organisms are fundamentally hydrogen transfer reac- tions. Postulated first by Wieland for respiration, as essentially a dehydrogena- tion of the respiratory substrate with oxy- gen or some other agent as the final hydro- gen acceptor, this concept has become ex- panded by Kluyver and others to its present broadest generalization. Thus all enzyme activity in metabolic processes serves primarily to facilitiate hydrogen transfer reactions. And it now appears that in the catabolic process this leads to the formation of products from which the building stones of cell growth and differen- tiation are directly synthesized by means of thermodynamically spontaneous reac- tions. This comprehensive generalization re-emphasizes the processes common to liv- ing things as the fundamental processes, whose elucidation provides our point of departure for an adequate understanding of the more complex vital phenomena.

In this respect the succeeding discussion on the viruses by Stanley is distinctly of

THE CELL AND PROTOPLASM

fundamental significance. It now appears that these entities represent a margin of animate nature beyond the limits of cellu- lar organization as commonly understood, yet they exhibit properties of organic syn- thesis and reproduction characteristic of the living cell. Evidently their size rela- tions alone are not definitive since they are larger than some well-known microbes but several times smaller than some protein molecules. Their apparently complete de- pendence on a living cell for their repro- duction would place them among obligate parasites whose nutrient requirements are highly specific and, at present, beyond ex- perimental duplication. Their essential nature, however, may have a counterpart in the chromosomal genes of the cell nu- cleus or in other known protoplasmic con- stituents such as the enzymes a relation- ship which would obviously carry funda- mental implications.

Some of the major advances in modern researches on the cell have had to do with its active protoplasmic constituents. Re- sumes of some recent results are presented in the three articles that follow on "En- zymes" by Theorell, on "Plant Hormones" by Went, and on "Vitamins" by Szent- Gyorgyi.

The common theme of these discussions demonstrates the essential relations be- tween these several active constituents. The common role of enzymes in the forma- tion or release of linkages within the car- bon chain is referable initially to the prosthetic groups. And for a number of well-known enzymes, the vitamin nature of their active groups is now established. Thus, Theorell has isolated the prosthetic groups of the "yellow enzymes" from the protein component by means of electro- phoresis and has identified this active group with Vitamin B2. It is now known also that Vitamin Bi, including its pyro- phosphate derivative, is identical with the prosthetic group of the enzyme carbox- ylase, and that the antipellagric vitamin is identical with the nicotinic acid amide which is the essential part of the prosthetic group of the dehydrogenases.

Enzyme specificity, however, is evidently

not due to the prosthetic group but to its associated protein molecule, thus denoting a relationship between activating and re- acting components of the cell which may come to account fundamentally for all bio- logical specificity. According to "Went, therefore, the more generalized activity of the growth hormones can be attributed to their identity with prosthetic groups. This was well illustrated by the multiple effects of auxin in cell elongation, bud inhibition, root formation, and probably other func- tions inside the plant. The initiation of these growth processes, or their inhibition, is traceable to the effect of diffusing or free- moving auxin on the translocation of other essential growth factors. But the specificity of this effect inheres in the co-growth fac- tors of the reacting tissues. The produc- tion of these essential active groups by some cells, such as those of the growing tip of a coleoptile, and the transport of these groups to other cells of the plant, which through cellular differentiation have lost this producing capacity, afford an excellent illustration of the interdependence of cells and the functional integration of the vari- ous differentiated organs. These relation- ships obviously underlie a unity in the plant organism that is entirely comparable with that in the animal.

These considerations of enzymes and growth hormones clearly indicate the essen- tial nature of the vitamins. As re-empha- sized by Szent-Gyorgyi, a vitamin is to be identified with the prosthetic group of en- zymes and it differs from a hormone, chiefly through the accident of nomenclature, ac- cording to the source of its production. Thus for rats or plants, ascorbic acid is not a vitamin since they themselves are able to synthesize it. In the same sense, thiamin is a vitamin for animals, a hormone in some plants, and a vitamin for other plants, de- pending only on their powers of synthesis. Obviously these relationships give further evidence of the fundamental unity in the plant and animal kingdoms, and in terms of the enzyme concept noted above, the vitamins constitute an important key to a better understanding of the essential na- ture of protoplasm and the cell.

THE CELL AND PROTOPLASM

The three concluding papers effectively linked this Symposium with the National Colloid Symposium which directly fol- lowed. These include: "The Molecular Structure of Protoplasm" by Sponsler, "Protoplasm and Colloids" by Heilbrunn, and "Structural Units" by Bernal.

The general concept of the living cell as an organized protoplasmic unit, which is stressed in foregoing papers, evidently pre- supposes for its protoplasm a fundamental architecture, i.e., an integrated spatial arrangement of the protoplasmic constitu- ents.

An analysis of this architecture is pre- sented by Sponsler as based on the known molecular constitution of protoplasm and computed from fairly well-established di- mensions of its protein chains and their linkages through hydrogen bonds. Assum- ing a degree of protoplasmic homogeneity, it is concluded that the protoplasm com- prises parallel protein chains, of dimen- sions about 1000 A by 10 A by 4.5 A, which are laterally united by water hydration centers, and which in turn compose a sponge-like framework intercalated with water containing the various solutes. From this elementary protoplasmic architecture is derived the fundamental pattern of the primordial cell which, through develop- mental differentiation, gives rise to the tissue cells and organs of the adult organ- ism, as recounted in the earlier discussions.

The colloidal properties of protoplasm and its cellular differentiation are vari- ously exemplified in the paper by Heil- brunn. His recent investigations have demonstrated especially a localization of calcium in the cortex of the cell which, upon appropriate stimulus, is released within and so effects a gelation of the pro-

toplasm involving contraction. Further evidences of this gelating effect were found upon exposing cut surfaces of cells to vari- ous concentrations of calcium salts. There- upon a reversible limiting membrane was formed on the cut surface, or a bulb-like contraction was locally induced, due to the penetrated calcium. Thus the age-old problem of contractility, a common prop- erty of protoplasm, may find its solution normally in the localization and release of calcium in the cell's cortex.

Recalling the emphasis given throughout the Symposium to the structural aspects of protoplasm, Bernal in the final paper urges that consideration of the energy relations is equally important since not only do the energies involved determine the sort of structure possible, but also their nature must be known in order to account for that structure. These energies relate primarily to the protein constituents of the proto- plasm, a model for which may be found in the tobacco mosaic virus when contained in known salt solutions. Here the virus enti- ties, which are long protein molecules, be- come oriented in striking spindle-like pat- terns, or tactoids, and their regular dis- tances apart vary directly with the concen- tration of the salt solution. Evidently long-range forces between the virus entities are operative through the ionic atmosphere of the surrounding medium with which the former are in equilibrium. The magni- tude and direction of forces inside the tac- toid pattern are different from those on the outside. These differences, in fact, account for the pattern formation. Apparently analogous forces may similarly account for the formation of the mitotic figure and the ensuing phenomena during the mitosis of the living cell.

CELL AND PROTOPLASM CONCEPTS; HISTORICAL ACCOUNT

By EDWIN G. CONKLIN

DEPARTMENT OF BIOLOGY, PRINCETON UNIVERSITY, PRINCETON, N. J.

I. Introduction

In preparing this historical account of the cell and protoplasm concepts I have had occasion to note how much less inter- esting such work is, based as it must be on the publications of others, than that which is first-hand observation. Indeed the latter is so much more agreeable that I suspect all historians must be tempted to mix their own thoughts and fancies with the actual records which they consult. The burden of looking up literature is one of the unpleas- ant features of modern research, and I quite sympathize with Jacques Loeb who used to say that he had no time or inclina- tion for it. Some one has said that the ancient Greeks were able to accomplish so much because they had no ancient lan- guages and literatures to master.

I suspect I was selected to give this his- torical review because I am probably the oldest living cytologist in America, now that our beloved master and foremost stu- dent of the cell. Professor Edmund B. Wilson, has passed away. But in spite of my age, which may seem venerable to some of you, I was not in at the birth of the cell theory and I have had to rely largely on literature in preparing the earlier part of this address. That portion of it which concerns the last half century falls within my own period of research work and with this account I have mingled some of my own observations, thoughts and fancies. Some of the earlier portions of this review repeat in part a paper entitled "Prede- cessors of Schleiden and Schwann" (1939) which I gave in a symposium on the cen- tenary of the cell theory at the Richmond, Virginia, meeting of the American Associa- tion for the Advancement of Science on December 27, 1938.

In the history of science, no less than in

that of the material universe, it is difficult if not impossible to find the real beginning of anything, for every event is the result of many preceding ones. In short there is no creation de novo in either the material or the intellectual universe. In an interesting article in the Scientific Monthly for De- cember 1937 entitled ''Who Invented It?" S. C. Gilfillan lists the numerous reputed inventors of the telegraph, the friction match, the barometer, the telephone, the airplane, steam boat, wireless and many other modern inventions, and as to the an- cient inventors of the wheel, the pulley, the boat, the sail, history is silent. And yet in each and all of these inventions we may be sure that there were many cooperators. The fact is that all discovery and all sci- ence are social phenomena and their prog- ress is possible only by the conscious or unconscious cooperation of many minds.

But it is difficult for human beings to keep in mind a multitude of persons or a multiplicity of causes. Consequently, even in science we find discoveries attributed to some one person, or phenomena ascribed to some one cause, whereas a more accurate account would recognize that they are the results of many persons and many causes. This difficulty of keeping in mind the many, joined with a common human ten- dency to make and worship heroes, leads to a great deal of historic error and injustice. We pick out some one person as the discov- erer or inventor or leader or soldier and build monuments to him, forgetting all his collaborators; we concentrate our devo- tions on the tomb of one unknown soldier, rather than on the armies of the fallen we celebrate anniversaries of births, dec- ades of science, jubilees of men and insti- tutions, centuries of progress, millennia of world history, as if these periods were inde- pendent of all others. We pick out some

CELL AND PROTOPLASM CONCEPTS

event of 1839 and celebrate its centenary in 1939, as if it had no antecedents as if it were a creation rather than an evolution.

These remarks apply with especial force to the origin of the cell theory. This sym- posium was designed in part to celebrate the centenary of the cell theory of Schleiden and Schwann, but the cell theory in all its fundamental features is older than either Schleiden or Schwann. Their cell theory was a special and, in important respects, an erroneous one. Since there is no present biological interest in their par- ticular theory, it is amazing that we still continue to call the great conception that the cell is the universal unit of organic structure and function after them, as if they were its sole discoverers, thus embalm- ing the names of two scientists, distin- guished for other discoveries, with one of their most serious blunders.

Greek philosophers and naturalists, and especially Aristotle, are said to have reached the conclusion "that animals and plants, complex as they may appear, are yet composed of comparatively few elemen- tary parts frequently repeated" (Locy 1908). But there is no doubt that these elementary parts were the roots, stems, nodes and internodes, the leaves and flow- ers of plants and the segments, organs and other parts of animals that were visible to the unaided eye. The discovery of the fun- damental elementary parts, the cells, was not possible before the invention of magni- fying lenses. It is probable that the use of simple lenses was known to the ancients. Pliny the Elder says that crystal globes filled with water were used as burning glasses. Seneca remarks that small letters are enlarged when seen through such glass globes. Nero, who was near-sighted, is said to have used a large emerald as a dis- tance glass. Coming to more recent times, spectacles for far or near sight were in- vented by d'Armato of Florence about 1300. Roger Bacon is said to have invented biconvex reading glasses in 1270, but ap- parently his invention remained unknown to the world for nearly 500 years. It has also been claimed that he invented the com- pound microscope, but if this be true it

also remained unknown until William Romaine Newbold deciphered the Voynich manuscript (1921).

The invention of the compound micro- scope is generally attributed to Hans and Zacharias Janssen, father and son, grind- ers of spectacles in Middleburg, Nether- lands, between 1590 and 1609. In 1610 Galileo made a microscope which he called Occhiale, ''that made a fly look as big as a hen"; and, as is well known, he also in- vented the telescope. The names micro- scope and telescope originated with Gio- vanni Faber of the Academia de Lincei about 1625 (Carpenter 1891).

II. Origin and Development of the Cell Theory

Cells were first seen, named, described and figured by Robert Hooke^ (1635-1703), an English scientist and architect, 170 years before the work of Schleiden and Schwann. Hooke had been a student at Christ Church, Oxford, and assistant to Robert Boyle, author of "The Sceptical Chymist, " 1661. In the year that the Royal Society received its charter, 1662, he was appointed curator of experiments and his duty was to furnish the Society at their weekly meetings with three or four consid- erable experiments. This he did satisfac- torily for forty years in spite of the fact that most of the instruments for experi- ments had to be made by himself. His ex- periments covered the whole range of the science of that time and led to a great

1 Hooke was a man of amazing versatility, one of the best mechanics and inventors of his age, a good mathematician and physicist and for thirty- eight years professor of geometry in Gresham Col- lege. After the great fire of London in 1666 he drew plans for the reconstruction of the burned over area which were approved by the Royal Soci- ety and the Common Council of London. He was appointed surveyor of the City and was responsible for widening the streets, and the building of the Monument, Bedlam Hospital, Montague House, College of Physicians et al. "His active, jealous mind conceived that almost every discovery of his time had been initiated by himself and this anxiety to claim priority induced Newton to suppress his treatise on optics until after Hooke 's death in 1703." (A. E. Shipley in Cambridge History of English Literature, -vol. 14, 1916.)

8

THE CELL AND PROTOPLASM

many discoveries of a fundamental nature. Unfortunately the very abundance of his experiments precluded a proper publica- tion of them. His experiments and dis- cussions at the meetings of the Royal So- ciety kept it alive and active during its formative period, and "it is scarcely an exaggeration to say that he was, histor- ically, the Creator of the Royal Society" (Robinson 1935).

In 1665, Hooke published a remarkable book entitled " Micrographia or Some Physiological Descriptions of Minute Bod- ies made by Magnifying Glasses." Using a compound microscope of excellent form which he had made himself, he described and figured sixty different types of micro- scopical objects. The section of the book of especial interest to us is entitled "Observ. XVIII. Of the Schematisme or Texture of Cork, and of the Cells and Pores of some other such frothy Bodies," which begins thus : " I took a good clear piece of cork and with a penknife sharpened as keen as a razor, I cut a piece of it off, and thereby left the surface of it exceedingly smooth, then examining it very diligently with a Microscope, methought I could perceive it to appear a little porous." Further study of thin sections showed that it was "all perforated and porous, much like a honey- combe ... in that these pores, or cells, were not very deep, but consisted of a great many little boxes, separated out of one con- tinued long pore by certain diaphragms." That he realized the importance of this observation is shown by the following: "I no sooner discerned these (which were in- deed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with any writer or person that had made any mention of them before this) but methought I had with the discov- ery of them presently hinted to me the true and intelligible reason of all the phenom- ena of cork" {i.e., its lightness, impervious- ness and compressibility). Of course he knew nothing of the way in which these cells were formed nor of the substance which had filled them in life, though he says of the cells of other plants, "In sev-

eral of those vegetables, whilst green, I have with my microscope plainly enough discovered these cells or pores filled with juices." Hooke counted three score of these cells of cork placed end ways in the eighteenth part of an inch and he calcu- lated that there were 1,166,400 in a square inch, or "above 12 hundred million in a cubic inch, a thing almost incredible." He showed that this cellular structure was not peculiar to cork for he subsequently found it in many other plant tissues.

Nehemiah Grew (1628-1711), English botanist and Secretary of the Royal Society (1677-1679), published numerous treatises on vegetable structures and functions. In his "Anatomy of Plants," published in 1672, he showed that the parenchyma of plants is composed of vesicles or closed spaces in a homogeneous ground mass. In 1675 and again in 1679, Marcello Malpighi (1628-1694), an Italian anatomist, physi- ologist and physician, published two folio volumes which justify his being called "creator of scientific botany." He distin- guished different plant tissues and called the cells of the parenchyma ' ' utricles. ' ' His fig- ures also indicated that even plant vessels are composed of series of utricles joined end to end.

The Dutch microscopist, Antony van Leeuwenhoek (1632-1723), was one of the most colorful and indefatigable students of microscopical objects during the late 17th and early 18th centuries. He used only simple lenses and it is amazing what he could see with them. In 1673 he sent his first paper to the Royal Society, and from that year until his death in 1723 the Royal Society received 375 letters and papers from him, while 27 more were sent to the French Academy of Sciences. In addition to his studies on numerous protozoa and protophyta and on the microscopic anat- omy of plants and animals, he discovered bacteria and spermatozoa and with his sim- ple lenses he thought he saw in the human spermatozoon the homunculus, or little man, postulated by the preformationists.

During the next hundred j^ears several botanists and anatomists saw and figured the utricles or vesicles in plants and ani-

CELL AND PROTOPLASM CONCEPTS

mals. The most notable of these was Cas- par Frederich Wolff (1733-1794). His thesis for the M.D. degree, published in 1759 when he was only 26 years old, was entitled Theoria Generationis and it marks an epoch in the study of the development of plants and animals. Wolff showed that in their development animals and plants are composed of "globules or utricles which may always be distinguished under a microscope of moderate magnification." He supposed that utricles arise as vacuoles in a homogeneous jelly. According to von Sachs, his was the most important work of the period between Grew, 1672, and Mirbel, 1808. "It was Wolff's doctrine of the for- mation of cellular structures in plants which was adopted in the main, by Mirbel ' ' (v. Sachs, History of Botany).

For more than one hundred years the words "utricles," "vesicles" or "glob- ules" were used to designate these con- stituent parts of animals and plants, and only in the beginning of the 19th century did Hooke's term "cell" again come into use. In 1808 and 1809, Brisseau de Mirbel (1776-1854), professor of botany in the Musee d 'Historic Naturelle in Paris, pub- lished a notable work on his theory of plant organization ("Theorie de 1 'organi- zation vegetale"). The general conclu- sions of this work were that "the plant is wholly formed of a continuous cellular membranous tissue." In a set of "Apho- risms" that he had prepared to accompany a large plate illustrating the finer structure of plants he wrote, "Plants are made up of cells, all parts of which are in continuity and form one and the same membranous tissue." It is apparent from this that while Mirbel recognized the universal pres- ence of cells in plants, he also regarded them as bound together in a membranous tissue.

Professor John H. Gerould (1922), in an important paper entitled "The Dawn of the Cell Theory," has shown that the great French naturalist, Lamarck (1744-1829), deserves to rank as one of the founders of the cell theory. In his Philosophie ZooU ogique published in 1809 he says: "No body can possess life if its containing parts