KARL, ERNST VON BAER.

THE CENTURY’S PROGRESS IN ANATOMY AND PHYSIOLOGY.

HENRY SMITH WILLIAMS, M.D

I. tablishing four great types of beiug, which focal points of the physiological lie called vertebrates, moll uses, articulates, -L world toward the close of the eigh- and radiates. Lamarck had shortly be- teenth century were Italy and England, fore established the broad distinction be- but when Spallanzani and Hunter passed tween animals with and those without a away, the scene shifted to France. The backbone; Cuvier’s classification divided time was peculiarly propitious, as the re- the latter—the invertebrates—into three cent advances in many lines of science minor groups. And this division, famil- had brought fresh data for the student of iar ever since to all students of zoology, animal life which were in need of classi- has only in very recent years been sup- fication, and as several minds capable of planted, and then not by revolution, but such a task were in the field, it was natu- by a further division, which the elaborate ral that great generalizations should have recent studies of lower forms of life seemed come to be quite the fashion. Thus it was to make desirable. thatCuviercameforwardwith a brand-new In the course of those studies of com- classification of the animal kingdom, es- parative anatomy which led to his new Yol. XCYI.—No. 574.—76 WILLIAM HYDE WOLLASTON. MATTHIAS JAKOB SCHLEIDEN. classification, Cuvier’s attention was call- Much the same thing may be said of ed constantly to the peculiar co-ordination another generalization regarding the an- of parts in each individual organism. imal body, which the brilliant young Thus an animal with sharp talons for French physician Marie Frangois Bichat catching living prey —as a member of the made in calling attention to the fact that cat tribe —has also sharp teeth, adapted each vertebrate organism, including man, for tearing up the flesh of its victim, and a has really two quite different sets of or- particular type of stomach, quite different gans—one set under volitional control, from that of hei’bivorous creatures. This and serving the end of locomotion, the adaptation of all the parts of the animal other removed from volitional control, to one another extends to the most diverse and serving the ends of the “vital pro- parts of the organism, and enables the cesses” of digestion, assimilation, and the skilled anatomist, from the observation of like. He called these sets of organs the a single typical part, to draw inferences animal system and the organic system, re- as to the structure of the entire animal—a spectively. The division thus pointed out fact which was of vast aid to Cuvier in was not quite new, for Grimaud, professor his studies of paleontology. It did not of physiology in the university of Mont- enable Cuvier, nor does it enable any one pellier, had earlier made what was sub- else, to reconstruct fully the extinct ani- stantially the same classification of the mal from observation of a single hone, as functions into “ internal or digestive and has sometimes been asserted, but what it external or locomotive”; but it was Bi- really does establish, in the hands of an chat’s exposition that gave currency to expert, is sufficiently astonishing. the idea. Of course this entire principle, in its Far more important, however, was an- broad outlines, is something with which other classification which Bichat put for- every student of anatomy had been famil- ward in his work on anatomy, published iar from the time when anatomy was first just at the beginning of the century. studied, but the full expression of the This was the division of all animal struc- “law of co-ordination,” as Cuvier called tures into what Bichat called tissues, and it, had never been explicitly made before; the pointing out that there are really only and notwithstanding its seeming obvious- a few kinds of these in the body, making ness, the exposition which Cuvier made up all the diverse organs. Thus muscu- of it in the introduction to his classical lar organs form one system ; membra- work on comparative anatomy, which was nous organs another; glandular organs a published during the first decade of the third; the vascular mechanism a fourth, century, ranks as a great discovery. It is and so on. The distinction is so obvious one of those generalizations which serve that it seems rather difficult to conceive as guide-posts to other discoveries. that it could have been overlooked by the THE CENTURY’S PROGRESS IN ANATOMY AND PHYSIOLOGY. 623 earliest anatomists; but, in point of fact, it In the attempt to overcome these diffi- is only obvious because now it has been culties, the foremost physical philosophers familiarly taught for almost a century. of the time came to the aid of the best It had neverbeen given explicit expression opticians. Very early in the century, before the time of Bichat, though it is Dr. (afterward Sir David) Brewster, the said that Bichat himself was somewhat renowned Scotch physicist, suggested that indebted for it to his master, the famous certain advantages might accrue from the ‘alienist, Pinel. use of such gems as have high refractive However that may be, it is certain that and low dispersive indices, in place of all subsequent anatomists have found Bi- lenses made of glass. Accordingly lenses chat’s classification of the tissues of the were made of diamond, of sapphire, and utmost value in their shidies of the ani- so on, and with some measure of success. mal functions. Subsequent advances were But in 1812 a much more important in- to show that the distinction between the novation was introduced by Dr. William various tissues is not really so fundamental as Bichat sup- posed, but that takes nothing from the practical value of the famous classification. 11. At the same time when these broad microscopical distinc- tions were being- drawn there were other workers who were striving to go even deeper into the intricacies of the animal mechanism with the aid of the microscope. This undertaking, however, was beset with very great optical difficulties, and for a long time little advance was made upon the work of preceding generations. Two great optical barriers, known technically as spherical and chromatic aberration—the one due to a failure of the rays of light to fail all in one plane MARIE FRANgOIS XAVIER BICHAT. David when focalized through a lens, From the medallion by dangers. the other due to the dispersive action of the lens in breaking the white Hyde Wollaston, one of the greatest and light into prismatic colors—confronted most versatile, and since the death of the makers of microscopic lenses, and Cavendish by far the most eccentric, of seemed all but insuperable. The making English natural philosophers. This was of achromatic lenses for telescopes had the suggestion to use two plano-convex been accomplished, it is true, by Dolland lenses, placed at a prescribed distance in the previous century, by the union of apart, in lieu of the single double convex lenses of crown glass with those of flint lens generally used. This combination glass, these two materials having different largely overcame the spherical aberration, indices of refraction and dispersion. But, and it gained immediate fame as the aside from the mechanical difficulties “ Wollaston doublet.” which arise when the lens is of the minute To obviate loss of light in such a doub- dimensions required for use with the mi- let from increase of reflecting surfaces, croscope, other perplexities are introduced Dr. Brewster suggested filling the inter- by the fact that the use of a wide pencil space between the two lenses with a of light is a desideratum, in order to gain cement having the same index of refrac- sufficient illumination when large mag- tion as the lenses themselves—an im- nification is to be secured. provement of manifest advantage. An 624 HARPER'S NEW MONTHLY MAGAZINE.

improvement yet more important was the compound microscope a practical im- made by Dr. Wollaston himself, in the plement instead of a scientific toy was the introduction of the diaphragm to limit English amateur optician Joseph Jackson the field of vision between the lenses, in- Lister. Combining mathematical know- stead of in front of the anterior lens. A ledge with mechanical ingenuity, and hav- pair of lenses thus equipped, Dr. Wollas- ing the practical aid of the celebrated op- ton called the periscopic microscope. Dr. tician Tulley, he devised formulae for the Brewster suggested that in such a lens combination of lenses of crown glass with the same object might be attained with others of flint glass, so adjusted that the greater ease by grinding an equatorial refractive errors of one were corrected or groove about a thick or globular lens compensated by the other, with the result and filling the groove with an opaque of producing lenses of hitherto unequalled cement. This arrangement found much powers of definition; lenses capable of favor, and came subsequently to be known showing an image highly magnified, yet as a Coddington lens, though Mr. Cod- relatively free from those distortions and dington laid no claim to being its in- fringes of color that had heretofore been ventor. so disastrous to true interpretation of Sir John Herschel, another of the very magnified structures. great physicists of the time, also gave Lister had begun bis studies of the lens attention to the problem of improving in 1824, but it was not until 1880 that he the microscope, and in 1821 he introduced contributed to the Royal Society the fa- what was called anaplanatic combination mous paper detailing his theories and ex- of lenses, in which, as the name implies, periments. Soon after this various Con- the spherical aberration was largely done tinental opticians who had long been away with. It was thought that the use working along similar lines took the mat- of this Herschel aplanatic combination as ter up, and their expositions, in particular an eye-piece, combined with the Wollas- that of Amici, introduced the improved ton doublet for the objective, came as compound microscope to the attention of near perfection as the compound micro- microscopists everywhere. And it re- scope was likely soon to come. But in quired but the most casual trial to con- reality the instrument thus constructed, vince the experienced observers that a new though doubtless superior to any prede- implement of scientific research had been cessor, was so defective that for practi- placed in their hands which carried them cal purposes the simple microscope, a long step nearer the observation of the such as the doublet or the Coddington, intimate physical processes which lie at was preferable to the more complicated the foundation of vital phenomena. For one. the physiologist, this perfection of the Many opticians, indeed, quite despaired compound microscope had the same sig- of ever being able to make a satisfactory nificance that the discovery of America refracting compound microscope, and had for the fifteenth-century geographers some of them had taken up anew Sir Isaac —it promised a veritable world of utterly Newton’s suggestion in reference to a re- novel revelations. Nor was the fulfil- flecting microscope. In particular, Pro- ment of that promise long delayed. fessor Giovanni Battista Amici, a very famous mathematician and practical opti- 111. cian of Modena, succeeded in construct- Indeed, so numerous and so important ing a reflecting microscope which was were the discoveries now made in the said to be superior to any compound mi- realm of minute anatomy that the rise of croscope of the time, though the events histology to the rank of an independent of the ensuing years were destined to rob science may be said to date from this pe- it of all but historical value. For there riod. Hitherto, ever since the discovery were others, fortunately, who did not de- of magnifying - glasses, there had been spair of the possibilities of the refracting here and there a man, sucli as Leuwen- microscope, and their efforts were des- hoek or Malpighi, gifted with exception- tined before long to be crowned with a al vision, and perhaps unusually happy degree of success not even dreamed of by in his conjectures, who made important any preceding generation. contributions to the knowledge of the The man to whom chief credit is due minute structure of organic tissues; but for directing those final steps that made now of a sudden it became possible for THE CENTURY'S PROGRESS IN ANATOMY AND PHYSIOLOGY. 625

the veriest tyro to confirm or refute the laborious observations of these pioneers, while the skilled ob- server could step easily beyond the barriers of vi- sion hitherto quite impassable. And so. naturally enough, the physiologists of the fourth decade of our century rushed as eagerly into the new realm of the microscope as, for example, their successors of to-day are exploring the realm of the X ray. Lister himself, who had become an eager inter- rogator of the instrument he had perfected, made many important discoveries, the most notable being his final settlement of the long-mooted question as to the true form of the red corpuscles of the hu- man blood. In reality, as everybody knows nowa- days, these are biconcave disks, but owing to their peculiar figure it is easily possible to misinterpret the appearances they present when seen through a poor lens, and though Dr. Thomas Young and vari- ous other observers had come near the truth very JEAN BAPTISTE DUMAS. regarding them, unanimity of opinion was possible only after the verdict of the perfected microscope was given. These blood corpuscles are so infinitesimal in size that something like five millions of them are found in each cubic millimetre of the blood, yet they are isolated particles, each having, so to speak, its own personality. This, of course, had been known to microscopists since the days of the earliest lenses. It had been noticed, too, by here and there an ob- server, that certain of the solid tissues seemed to present something of a granular texture, as if they too, in their ultimate constitution, were made up of particles. And now, as better and better lenses were constructed, this idea gained ground con- stantly, though for a time no one saw its full sig- nificance. In the case of vegetable tissues, indeed, the fact that little particles encased in a membra- nous covering, and called cells, are the ultimate visible units of structure had long been known. CLAUDE BERNARD. But it was supposed that animal tissues differed radically from this construction. The elementary particles of vegetables 11 were regarded to a certain extent as individuals which composed the entire plant, whilst, on the other hand, no such view was taken of the elementary parts of animals.” In the year 1838 a further insight into the nature of the ultimate particles of plants was gained through the observation of the English microscop- ist Robert Brown, who, in the course of his micro- scopic studies of the epidermis of orchids, discovered in the cells “an opaque spot,” which he named the “ nucleus. Doubtless the same spot ” had been seen often enough before by other observers, but Brown was the first to recognize it as a component part of the vegetable cell, and to give it a name. That this newly recognized structure must be important in the economy of the cell was recognized by Brown himself, and by the celebrated German Meyen, who with it in his on vegetable physiology, WILLIAM BENJAMIN CARPENTER. dealt work Photograph by Elliott and Frj, London. 626 HARPER’S NEW MONTHLY MAGAZINE

was puzzling over certain details of ani- mal histology which he could not clear- ly explain. His great teacher, Johan- nes Muller, had called attention to the strange resemblance to vegetable cells shown by certain cells of the chorda dorsalis (the embryonic cord fromwhich the spinal column is developed), and Schwann himself had discovered a cor- responding similarity in the branchial cartilage of a tadpole. Then,too, the re- searches of Friedrich Henle had shown that the particles that make up the epi- dermis of animals are very cell-like in appearance. Indeed, the cell-like char- acter of certain animal tissues had come to be matter of common note among students of minute anatomy. Schwann felt that this similarity could not be mere coincidence, but he had gained no clew to further insight until Schleiden called his attention to the nucleus. Then at once he reasoned that if there really is the correspon- dence between vegetable and animal tissues that he suspected, and if the nu- HUGO YON SIOHL. cleus is so important in the vegetable cell as Schleiden believed, the nucleus should also be found in the ultimate published not long afterwards; but it re- particles of animal tissues. mained for another German, the professor Schwann’s researches soon showed the of botany in the university of Jena, Dr. entire correctness of this assumption. A M. J. Schleiden, to bring the nucleus to closer study of animal tissues under the popular attention, and to assert its all- microscope showed, particularly in the importance in the economy of the cell. case of embryonic tissues, that “opaque Schleiden freely acknowledged bis in- spots” such as Schleiden described are debtedness to Brown for first knowledge really to be found there in abundance of the nucleus, but he soon carried his —forming, indeed, a most characteristic studies of that structure far beyond those phase of the structure. The location of of its discoverer. He came to believe these nuclei at comparatively regular in- that the nucleus is really the most im- tervals suggested that they are found in portant portion of the cell, in that it is definite compartments of the tissue, as the original structure from which the re- Schleiden had shown to be the case with mainder of the cell is developed. Hence vegetables; indeed, the walls that separa- he named it the cytoblast. He outlined ted such cell-like compartments one from his views in an epochal paper published another were in some cases visible. Par- in Muller’s Archives in 1838, under title ticularly was this found to be the case of “ Beitrage zur Phytogenesis.” This with embryonic tissues, and the study of paper is in itself of value, yet the most these soon convinced Schwann that his important outgrowth of Schleiden’s ob- original surmise had been correct, and servations of the nucleus did not spring that all animal tissues are in their incipi- from his own labors, but from those of a ency composed of particles not unlike the friend to whom he mentioned his discov- ultimate particles of vegetables—in short, eries the year previous to their publi- of what the botanists termed cells. Adopt- cation. This friend was Dr. Theodor ing this name, Schwann propounded what Schwann, professor of physiology in the soon became famous as his cell theory, university of Louvain. under title of Mikroskopische Untersu- At the moment when these observa- chungen iiber die Uebereinstimmung in tions were communicated to him Schwann dev Structur und dem Wachsthum der THE CENTURY’S PROGRESS IN ANATOMY AND PHYSIOLOGY. 627 Thieve und Pflanzen. So expeditious had been his work, that this book was published early in 1839, only a few months after the appearance of Schlei- den’s paper. As the title suggests, the main idea that actuated Schwann was to unify vegetable and animal tissues. Accept- ing cell-structure as the basis of all vegetable tissues, he sought to show that the same is true of animal tissues, all the seeming diversities of fibre be- ing but the alteration and development of what were originally simple cells. And by cell Schwann meant, as did Schleiden also, what the word ordi- narily implies—a cavity walled in on ail sides. He conceived that the ulti- mate constituents of all tissues were really such minute cavities, the most important part of which was the cell wall, with its associated nucleus. He knew, indeed, that the cell might be filled with fluid contents, but he re- garded these as relatively subordinate in importance to This, the wall itself. JOHANNES MULLER. however, did not apply to the nucleus, which was supposed to lie against the cell wall, and in the beginning to gen- erate it. Subsequently the wall might Dumortier, Purkinje, and Muller, all of grow so rapidly as to dissociate itself from whom Schwann himself had quoted. its contents, thus becoming a hollow bub- Moreover, there were various physiolo- ble or true cell; but the nucleus, as long gists who earlier than any of these had as it lasted, was supposed to continue in foreshadowed the cell theory; notably contact with the cell wall. Schleiden had Kaspar Friedrich Wolff toward the close even supposed the nucleus to be a con- of the previous century, and Treviranus stituent part of the wall, sometimes lying about 1807. But, as we have seen in so enclosed between two layers of its sub- many other departments of science, it is stance, and Schwann quoted this view one thing to foreshadow a discovery, it with seeming approval. Schwann be- is quite another to give it full expression lieved, however, that in the mature cell and make it germinal of other discov- the nucleus ceased to be functional, and eries. And when Schwann put forward disappeared. the explicit claim that “there is one uni- The main thesis as to the similarity of versal principle of development for the development of vegetable and animal elementary parts of organisms, however tissues, and the cellular nature of the ul- different, and this principle is the for- timateconstitution of both, was supported mation of cells,” he enunciated a doc- by a mass of carefully gathered evidence trine which was for all practical purposes which a multitude of microscopists at absolutely new, and opened up a novel once confirmed, so Schwann’s work be- field for the microscopists to enter. A came a classic almost from the moment most important era in physiology dates of its publication. Of course various from the publication of his book in 1889. other workers at once disputed Schwann’s claim to priority of discovery, in particu- IY. lar the English microscopist Valentin, That Schwann should have gone to who asserted, not without some show of embryonic tissues for the establishment justice, that he was working closely along of his ideas was no doubt due very large- the same lines. But so, for that matter, ly to the influence of the great Russian wei*e numerous others, as Henle, Turpin, Karl Ernst von Baer, who about ten 628 HARPER’S NEW MONTHLY MAGAZINE,

was universally ac- cepted. Yet tlie full measure of the affinity between the two classes of cells was not for some time generally apprehended. Indeed, since the sub- stance that composes the cell walls of plants is manifestly very dif- ferent from the limit- ing membrane of the animal cell, it was nat- ural, so long as the wall was considered the most essential part of the structure, that the divergence between the two classes of cells should seem very pro- nounced. And for a time this was the con- ception of the matter that was uniformly ac- cepted. But as time went on many observ- ers had their attention called to the peculiar characteristics of the contents of the cell, and were led to ask themselves whether these might not be more important than had been supposed. In particular Dr. Hugo MAX SCHULTZE. von Mold, professor of botany in tbe universi- years earlier bad published the first part ty of Tubingen, in the course of his ex- of his celebrated work on embryology, haustive studies of the vegetable cell, was and whose ideas were rapidly gaining impressed with the peculiar and charac- ground, thanks largely to the advocacy teristic appearance of the cell contents. of a few men, notably Johannes Muller He observed universally within the cell “ in Germany, and William B. Carpenter an opaque, viscid fluid, having granules in England, and to the fact that the im- intermingled in it,” which made up the proved microscope had made minute an- main substance of the cell, and which atomy popular. Schwann’s researches particularly impressed him because under made it plain that the best field for the certain conditions it could be seen to be study of tbe animal cell is here, and a actively in motion, its parts separated into host of explorers entered the field. The filamentous streams. result of their observations was, in the Von Mohl called attention to the fact main, to confirm the claims of Sch wann that this motion of the cell contents had as to the universal prevalence of the cell. been observed as long ago as 1774 by The long-current idea that animal tissues Bonaventura Corti, and rediscovered in grow only as a sort of deposit from the 1807 by Treviranus, and that these ob- blood-vessels was now discarded, and the servers had described the phenomenon fact of so-called plantlike growth of ani- under the “most unsuitable name of ‘ro- mal cells, for which Schwann contended, tation of the cell sap.’ ” Von Mohl rec- THE CENTURY’S PROGRESS IN ANATOMY AND PHYSIOLOGY. 629 ognized that the streaming substance was vellously similar in appearance and gen- something quite different from sap. He eral properties. The closer the observa- asserted that the nucleus of the cell lies tion the more striking seemed this simi- within this substance, and not attached larity; and finally, about 1860, it was to the cell wall as Schleiden had contend- demonstrated by Heinrich de Bary and by ed. He saw, too, that the chlorophyl Max Schultze that the two are to all in- granules, and all other of the cell con- tents and purposes identical. Even ear- tents, are incorporated with the “ opaque, lier, Remak had reached a similar con- viscid fluid,” and in 1846 he had become clusion, and applied von Mohl’s word so impressed with the importance of this protoplasm to animal cell contents, and universal cell substance that he gave it now this application soon became univer- the name of protoplasm. Yet in so doing sal. Thenceforth this protoplasm was to he had no intention of subordinating the assume the utmost importance in the phy- cell wall. The fact that Payen, in 1844, siological world, being recognized as the had demonstrated that the cell walls of universal “physical basis of life,” veg- all vegetables, high or low, are composed etable and animal alike. This amounted largely of one substance, cellulose, tend- to the logical extension and culmination ed to strengthen the position of the cell of Schwann’s doctrine as to the similarity wall as the really essential structure, of of development of the two animate king- which the protoplasmic contents were doms. Yet at the same time it was in only subsidiary products. effect the banishment of the cell that Meantime, however, the students of an- Schwann had defined. The word cell imal histology were more and more im- was retained, it is true, but it no longer pressed with the seeming preponderance signified a minute cavity. It now im- of cell contents over cell walls in the tis- plied, as Schultze defined it, “a small sues they studied. They too found the mass of protoplasm endowed with the at- cell to be filled with a viscid, slimy fluid, tributes of life.” This definition was des- capable of motion. To this Dujardin tined presently to meet with yet another gave the name of sarcode. Presently it modification, as we shall see; but the came to be known, through the labors of conception of the protoplasmic mass as Kolliker, Nageli, Bischoff, and various the essential ultimate structure, which others, that there are numerous lower might or might not surround itself with forms of animal life which seem to be a protective covering, was a permanent composed of this sarcode, without any addition to physiological knowledge. The cell wall whatever. The same thing earlier idea had, in effect, declared the seemed to be true of certain cells of high- shell the most important part of the egg; er organisms, as the blood corpuscles. this developed view assigned to the yolk Particularly in the case of cells that its true position. change their shape markedly, moving In one other important regard the the- about in consequence of the streaming of ory of Schleiden and Schwann now be- xheir sarcode, did it seem certain that no came modified. This referred to the cell wall is present; or that, if present, its origin of the cell. Schwann had regard- role must he insignificant. ed cell growth as a kind of crystalliza- And so histologists came to question tion, beginning with the deposit of a whether, after all, the cell contents rather nucleus about a granule in the intercel- than the enclosing wall must not be the lular substance the cytoblastema, as really essential structure, and the weight Schleiden called it. But von Mohl, as of increasing observations finally left no early as 1835, had called attention to the escape from the conclusion that such is formation of new vegetable cells through really the case. But attention being thus the division of a pre-existing cell. Ehren- focalized on the cell contents, it was at berg, another high authority of the time, once apparent that there is a far closer contended that no such division occurs, similarity between the ultimate particles and the matter was still in dispute when of vegetables and those of animals than Schleiden came forward with his discov- had been supposed. Cellulose and ani- ery of so-called free cell formation with- mal membrane being now regarded as in the parent cell, and this for a long mere by-products, the way was clear for time diverted attention from the process the recognition of the fact that vegetable of division which von Mohl had de- protoplasm and animal sarcode are mar- scribed. All manner of schemes of cell Vol. XCVI.— No. 574.-77 630 HARPER’S NEW MONTHLY MAGAZINE. formation were put forward during the cell, however specialized, ever forget alto- ensuing years by a multitude of observ- gether any one of its primordial func- ers, and gained currency notwithstanding tions or capacities. All physiology, then, von Mold’s reiterated contention that properly interpreted, becomes merely a there are really but two ways in which study of cellular activities; and the de- the formation of new cells takes place, velopment of the cell theory takes its namely, “ first, through division of older place as the great central generalization cells; secondly, through the formation of in physiology of our century. Something secondary cells lying free in the cavity of of the later developments of this theory a cell.” we shall see in another connection. But gradually the researches of such Y. accurate observers as Unger, Nageli, Kdlliker, Reichart, and Remak tended to Just at the time when the microscope confirm the opinion of von Mold that was opening up the paths that were to cells spring only from cells, and finally lead to the wonderful cell theory, another Rudolf Virchow brought the matter to novel line of interrogation of the living demonstration about 1860. His Omnis organism was being put forward by a dif- cellula e cellula became from that time ferent set of observers. Two great schools one of the accepted data of physiology. of physiological chemistry had arisen This was supplemented a little later by —one under guidance of Liebig and Fleming’s Omnis nucleus e nucleo, when Wohler in Germany, the other dominated still more refined methods of observation by the great French master Jean Baptiste had shown that the part of the cell which Dumas. Liebig had at one time contem- always first undergoes change prepara- plated the study of medicine, and Dumas tory to new cell formation is the all-es- had achieved distinction in connection sential nucleus. Thus the nucleus was with Prevost at Geneva in the field of I’estored to the important position which pure physiology before he turned his at- Schwann and Schleiden had given it, but tention especially to chemistry. Both with greatly altered significance. In- these masters, therefore, and Wohler as stead of being a structure generated de well, found absorbing interest in those novo from non - cellular substance, and phases of chemistry that have to do with disappearing as soon as its function of the functions of living tissues; and it was cell-formation was accomplished, the nu- largely through their efforts and the la- cleus was now known as the central and bors of their followers that the prevalent permanent feature of every cell, inde- idea that vital processes are dominated by structible while the cell lives; itself the unique laws was discarded and physiology division - product of a pre - existing nu- was brought within the recognized prov- cleus, and the parent, by division of its ince of the chemist. So at about the substance, of other generations of nuclei. time when the microscope had taught The word cell received a final definition that the cell is the really essential struc- as “ a small mass of protoplasm supplied ture of the living organism, the chemists with a nucleus.” had come to understand that every func- In this widened and culminating gen- tion of the organism is really the expres- eral view of the cell theory it became sion of a chemical change—that each cell clear that every animate organism, ani- is, in short, a miniature chemical labora- mal or vegetable, is but a cluster of nu- tory. And it was this combined point of cleated cells, all of which, in each indi- view of anatomist and chemist, this union vidual case, are the direct descendants of of hitherto dissociated forces, that made a single primordial cell of the ovum. In possible the inroads into the unexplored the developed individuals of higher or- fields of physiology that were effected ganisms the successive generations of toward the middle of our century. cells become marvellously diversified in One of the first subjects reinvestigated form and in specific functions; there is a and brought to proximal solution was the wonderful division of labor, special func- long-mooted question of the digestion of tions being chiefly relegated to definite foods. SpallanzaniandHunter had shown groups of cells; but from first to last there in the previous century that digestion is is no function developed that is not pres- in some sort a solution of foods; but lit- ent, in a primitive way, in every cell, tle advance was made upon their work however isolated; nor does the developed until 1824, when Prout detected the pres- THE CENTURY’S PROGRESS IN ANATOMY AND PHYSIOLOGY. 631 ence of hydrochloric acid in the gastric off during respiration the chemists of the juice. A decade later Sprott and Boyd age of Priestley and Lavoisier had in- detected the existence of peculiar glands deed made clear, but the mistaken notion in the gastric mucous membrane; and prevailed that it was in the lungs them- Cagniard ia Tour and Schwann indepen- selves that the important burning of fuel dently discovered that the really active occurs, of which carbonic acid is a chief principle of the gastric juice is a sub- product. But now that attention had stance which was named pepsin, and been called to the importance of the which was shown by Schwann to be ac- ultimate cell, this misconception could tive in the presence of hydrochloric acid. not long hold its ground, and as early Almost coincidently, in 1836, it was dis- as 1842, Liebig, in the course of his stud- covered by Purkinje and Pappenheim ies of animal heat, became convinced that that another organ than the stomach—the it is not in the lungs, but in the ultimate pancreas, namely—has a share in diges- tissues to which they are tributai*y, that tion, and in the course of the ensuing the true consumption of fuel takes place. decade it came to be known, through the Reviving Lavoisier’s idea, with modifica- efforts of Eberle, Valentin, and Claude tions and additions, Liebig contended, Bernard, that this organ is all-important and in the face of opposition finally de- in the digestion of starchy and fatty foods. monstrated, that the soui’ce of animal heat It was foundytoo, that the liver and the is really the consumption of the fuel intestinal glands have each an important taken in through the stomach and the share in the work of preparing foods for lungs. He showed that all the activities absorption, as also has the saliva—that, of life are really the product of energy in short, a coalition of forces is necessary liberated solely through destructive pro- for the digestion of all ordinary foods cesses, amounting, broadly speaking, to taken into the stomach. combustion occurring in the ultimate And the chemists soon discovered that cells of the organism. in each one of the essential digestive Further researches showed that the juices there is at least one substance hav- carriers of oxygen, from the time of its ing certain resemblances to pepsin,though absorption in the lungs till its liberation acting on different kinds of food. The in the ultimate tissues, are the red cor- point of resemblance between all these puscles, whose function had been supposed essential digestive agents is that each has to be the mechanical one of mixing of the remarkable property of acting on the blood. It transpired that the red relatively enormous quantities of the sub- corpuscles are composed chiefly of a sub- stance which it can digest without itself stance which Kiihne first isolated in crys- being destroyed or apparently even al- talline form in 1865, and which was named tered. In virtue of this strange property, haemoglobin—a substance which has a pepsin and the allied substances were marvellous affinity for oxygen, seizing spoken of as ferments, but more recently on it eagerly at the lungs, yet giving it it is customary to distinguish them from up with equal readiness when coursing such organized ferments as yeast by desig- among the remote cells of the body. nating them enzymes. The isolation of When freighted with oxygen it becomes these enzymes,and an appreciation of their oxyhasmoglobin, and is red in color; mode of action, mark a long step toward when freed from its oxygen it takes a the solution of the riddle of digestion, purple hue; hence the widely different but it must be added that we are still appearance of arterial and venous blood, quite in the dark as to the real ultimate which so puzzled the early physiologists. nature of their strange activity. This proof of the vitally important role In a comprehensive view, the digestive played by the red blood corpuscles led, organs, taken as a whole, are a gateway naturally, to renewed studies of these in- between the outside world and the more finitesimal bodies. It was found that they intimate cells of the organism. Another may vary greatly in number at diffei’ent equally important gateway is furnished periods in the life of the same individual, by the lungs, and here also there was proving that they may be both developed much obscurity about the exact method and destroyed in the adult organism. In- of functioning at the time of the revival deed, extended observations left no rea- of physiological chemistry. That oxy- son to doubt that the process of corpuscle gen is consumed and carbonic acid given formation and destruction may be a per- 633 HARPER’S NEW MONTHLY MAGAZINE. fectly normal one; that, in short, every a ductless organ, but the quantity of its red blood corpuscle runs its course and biliary output seems utterly dispropor- dies like any more elaborate organism. tionate to its enormous size, particularly They are'formed constantly in the red when it is considered that in the case of marrow of bones, and are destroyed in the human species the liver contains nor- the liver, where they contribute to the mally about one-fifth of all the blood in formation of the coloring matter of the the entire body. Bernard discovered that bile. Whether there are other seats of the blood undergoes a change of composi- such manufacture and destruction of the tion in passing through the liver. The corpuscles is not yet fully determined. liver cells (the peculiar forms of which Nor are histologists agreed as to whether had been described by Purkiuje, Henle. the red blood corpuscles themselves are andDutrochet about 1838) have the power to be regarded as true cells, or merely as to convert certain of the substances that fragments of cells budded out from a true come to them into a starchlike com- cell for a special purpose; but, in either pound called glycogen, and to store this case, there is not the slightest doubt that substance away till it is needed by the the chief function of the red corpuscle is organism. This capacity of the liver to carry oxygen. cells is quite independent of the bile- If the oxygen is taken to the ultimate making power of the same cells; hence cells before combining with the combus- the discovery of this glycogenic function tibles it is to consume, it goes without showed that an organ may have more saying that these combustibles themselves than one pronounced and important spe- must be carried there also. Nor could it cific function. But its chief importance be in doubt that the chiefest of these ul- was in giving a clew to those intermedi- timate tissues, as regards quantity of fuel ate processes between digestion and final required, are the muscles. A general and assimilation that are now known to be of comprehensive view of the organism in- such vital significance in the economy of cludes, then, digestive apparatus and lungs the organism. as the channels of fuel-supply; blood In the forty-odd years that have elapsed and lymph channels as the transporta- since this pioneer observation of Bernard, tion system; and muscle cells, united into numerous facts have come to light show- muscle fibres, as the consumption fur- ing the extreme importance of such inter- naces, where fuel is burned and energy mediatealterations of food-supplies in the transformed and rendered available for blood as that performed by the liver. It the purposes of the organism, supple- has been shown that the pancreas, the mented by a set of excretory organs, spleen, the thyroid gland, the suprarenal through which the waste products—the capsules, each in its own way, are absolute- ashes—are eliminated from the system. ly essential to the health of the organism, But there remain, broadly speaking, through metabolic changes which they two other sets of organs whose size de- alone seem capable of performing; and monstrates their importance in the econo- it is suspected that various other tissues, my of the organism, yet whose functions including even the muscles themselves, are not accounted for in this synopsis. have somewhat similar metabolic capaci- These are those glandlike organs, such ties in addition to their recognized func- as the spleen, which have no duct and tions. But so extremely intricate is the produce no visible secretions; and the chemistry of the substances involved that nervous mechanism, whose central organs in no single case has the exact nature of are the brain and spinal cord. What of- the metabolisms wrought by these organs fices do these sets of organs perform in been fully made out. Each is in its way the great labor-specializing aggregation a chemical laboratory indispensable to of cells which we call a living organism? the right conduct of the organism, but As regards the ductless glands, the first the precise nature of its operations re- clew to their function was given when mains inscrutable. The vast importance the great Frenchman Claude Bernard of the operations of these intermediate (the man of whom his admirers loved to organs is unquestioned. say, “he is not a physiologist merely; he A consideration of the functions of that is physiology itself ”) discovered what is other set of organs known collectively spoken of as the glycogenic function of as the nervous system is reserved for a the liver. The liver itself, indeed, is not later paper. fa& _ JBk it Iplm M l||l

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No. 574. MARCH, 1898. 35 Cents.

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