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 
lie called vertebrates, moll uses, articulates, 
and radiates. Lamarck had shortly be- 
fore established the broad distinction be- 
tween animals with and those without a 
backbone; Cuvier’s classification divided 
the latter—the invertebrates—into three 
minor groups. And this division, famil- 
iar ever since to all students of zoology, 
has only in very recent years been sup- 
planted, and then not by revolution, but 
by a further division, which the elaborate 
recent studies of lower forms of life seemed 
to make desirable. 
In the course of those studies of com- 
parative anatomy which led to his new 
focal points of the physiological 
-L world toward the close of the eigh- 
teenth century were Italy and England, 
but when Spallanzani and Hunter passed 
away, the scene shifted to France. The 
time was peculiarly propitious, as the re- 
cent advances in many lines of science 
had brought fresh data for the student of 
animal life which were in need of classi- 
fication, and as several minds capable of 
such a task were in the field, it was natu- 
ral that great generalizations should have 
come to be quite the fashion. Thus it was 
thatCuviercameforward with a brand-new 
classification of the animal kingdom, es- 
Yol. XCYI.—No. 574.—76 WILLIAM HYDE WOLLASTON. 
MATTHIAS JAKOB SCHLEIDEN. 
classification, Cuvier’s attention was call- 
ed constantly to the peculiar co-ordination 
of parts in each individual organism. 
Thus an animal with sharp talons for 
catching living prey—as a member of the 
cat tribe—has also sharp teeth, adapted 
for tearing up the flesh of its victim, and a 
particular type of stomach, quite different 
from that of hei’bivorous creatures. This 
adaptation of all the parts of the animal 
to one another extends to the most diverse 
parts of the organism, and enables the 
skilled anatomist, from the observation of 
a single typical part, to draw inferences 
as to the structure of the entire animal—a 
fact which was of vast aid to Cuvier in 
his studies of paleontology. It did not 
enable Cuvier, nor does it enable any one 
else, to reconstruct fully the extinct ani- 
mal from observation of a single hone, as 
has sometimes been asserted, but what it 
really does establish, in the hands of an 
expert, is sufficiently astonishing. 
Of course this entire principle, in its 
broad outlines, is something with which 
every student of anatomy had been famil- 
iar from the time when anatomy was first 
studied, but the full expression of the 
“law of co-ordination,” as Cuvier called 
it, had never been explicitly made before; 
and notwithstanding its seeming obvious- 
ness, the exposition which Cuvier made 
of it in the introduction to his classical 
work on comparative anatomy, which was 
published during the first decade of the 
century, ranks as a great discovery. It is 
one of those generalizations which serve 
as guide-posts to other discoveries. 
Much the same thing may be said of 
another generalization regarding the an- 
imal body, which the brilliant young 
French physician Marie Frangois Bichat 
made in calling attention to the fact that 
each vertebrate organism, including man, 
has really two quite different sets of or- 
gans—one set under volitional control, 
and serving the end of locomotion, the 
other removed from volitional control, 
and serving the ends of the “vital pro- 
cesses” of digestion, assimilation, and the 
like. He called these sets of organs the 
animal system and the organic system, re- 
spectively. The division thus pointed out 
was not quite new, for Grimaud, professor 
of physiology in the university of Mont- 
pellier, had earlier made what was sub- 
stantially the same classification of the 
functions into “ internal or digestive and 
external or locomotive”; but it was Bi- 
chat’s exposition that gave currency to 
the idea. 
Far more important, however, was an- 
other classification which Bichat put for- 
ward in his work on anatomy, published 
just at the beginning of the century. 
This was the division of all animal struc- 
tures into what Bichat called tissues, and 
the pointing out that there are really only 
a few kinds of these in the body, making 
up all the diverse organs. Thus muscu- 
lar organs form one system ; membra- 
nous organs another; glandular organs a 
third; the vascular mechanism a fourth, 
and so on. The distinction is so obvious 
that it seems rather difficult to conceive 
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 
is only obvious because now it has been 
familiarly taught for almost a century. 
It had never been given explicit expression 
before the time of Bichat, though it is 
said that Bichat himself was somewhat 
indebted for it to his master, the famous 
‘alienist, Pinel. 
However that may be, it is certain that 
all subsequent anatomists have found Bi- 
chat’s classification of the tissues of the 
utmost value in their shidies of the ani- 
mal functions. Subsequent advances were 
to show that the distinction between the 
various tissues is not really so 
fundamental as Bichat sup- 
posed, but that takes nothing 
from the practical value of the 
famous classification. 
In the attempt to overcome these diffi- 
culties, the foremost physical philosophers 
of the time came to the aid of the best 
opticians. Very early in the century, 
Dr. (afterward Sir David) Brewster, the 
renowned Scotch physicist, suggested that 
certain advantages might accrue from the 
use of such gems as have high refractive 
and low dispersive indices, in place of 
lenses made of glass. Accordingly lenses 
were made of diamond, of sapphire, and 
so on, and with some measure of success. 
But in 1812 a much more important in- 
novation was introduced by Dr. William 
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 
when focalized through a lens, 
the other due to the dispersive 
action of the lens in breaking the white 
light into prismatic colors—confronted 
the makers of microscopic lenses, and 
seemed all but insuperable. The making 
of achromatic lenses for telescopes had 
been accomplished, it is true, by Dolland 
in the previous century, by the union of 
lenses of crown glass with those of flint 
glass, these two materials having different 
indices of refraction and dispersion. But, 
aside from the mechanical difficulties 
which arise when the lens is of the minute 
dimensions required for use with the mi- 
croscope, other perplexities are introduced 
by the fact that the use of a wide pencil 
of light is a desideratum, in order to gain 
sufficient illumination when large mag- 
nification is to be secured. 
MARIE FRANgOIS XAVIER BICHAT. 
From the medallion by David dangers. 
Hyde Wollaston, one of the greatest and 
most versatile, and since the death of 
Cavendish by far the most eccentric, of 
English natural philosophers. This was 
the suggestion to use two plano-convex 
lenses, placed at a prescribed distance 
apart, in lieu of the single double convex 
lens generally used. This combination 
largely overcame the spherical aberration, 
and it gained immediate fame as the 
“ Wollaston doublet.” 
To obviate loss of light in such a doub- 
let from increase of reflecting surfaces, 
Dr. Brewster suggested filling the inter- 
space between the two lenses with a 
cement having the same index of refrac- 
tion as the lenses themselves—an im- 
provement of manifest advantage. An 624 
HARPER'S NEW MONTHLY MAGAZINE. 
improvement yet more important was 
made by Dr. Wollaston himself, in the 
introduction of the diaphragm to limit 
the field of vision between the lenses, in- 
stead of in front of the anterior lens. A 
pair of lenses thus equipped, Dr. Wollas- 
ton called the periscopic microscope. Dr. 
Brewster suggested that in such a lens 
the same object might be attained with 
greater ease by grinding an equatorial 
groove about a thick or globular lens 
and filling the groove with an opaque 
cement. This arrangement found much 
favor, and came subsequently to be known 
as a Coddington lens, though Mr. Cod- 
dington laid no claim to being its in- 
ventor. 
the compound microscope a practical im- 
plement instead of a scientific toy was the 
English amateur optician Joseph Jackson 
Lister. Combining mathematical know- 
ledge with mechanical ingenuity, and hav- 
ing the practical aid of the celebrated op- 
tician Tulley, he devised formulae for the 
combination of lenses of crown glass with 
others of flint glass, so adjusted that the 
refractive errors of one were corrected or 
compensated by the other, with the result 
of producing lenses of hitherto unequalled 
powers of definition; lenses capable of 
showing an image highly magnified, yet 
relatively free from those distortions and 
fringes of color that had heretofore been 
so disastrous to true interpretation of 
magnified structures. 
Sir John Herschel, another of the very 
great physicists of the time, also gave 
attention to the problem of improving 
the microscope, and in 1821 he introduced 
what was called anaplanatic combination 
of lenses, in which, as the name implies, 
the spherical aberration was largely done 
away with. It was thought that the use 
of this Herschel aplanatic combination as 
an eye-piece, combined with the Wollas- 
ton doublet for the objective, came as 
near perfection as the compound micro- 
scope was likely soon to come. But in 
reality the instrument thus constructed, 
though doubtless superior to any prede- 
cessor, was so defective that for practi- 
cal purposes the simple microscope, 
such as the doublet or the Coddington, 
was preferable to the more complicated 
one. 
Lister had begun bis studies of the lens 
in 1824, but it was not until 1880 that he 
contributed to the Royal Society the fa- 
mous paper detailing his theories and ex- 
periments. Soon after this various Con- 
tinental opticians who had long been 
working along similar lines took the mat- 
ter up, and their expositions, in particular 
that of Amici, introduced the improved 
compound microscope to the attention of 
microscopists everywhere. And it re- 
quired but the most casual trial to con- 
vince the experienced observers that a new 
implement of scientific research had been 
placed in their hands which carried them 
a long step nearer the observation of the 
intimate physical processes which lie at 
the foundation of vital phenomena. For 
the physiologist, this perfection of the 
compound microscope had the same sig- 
nificance that the discovery of America 
had for the fifteenth-century geographers 
—it promised a veritable world of utterly 
novel revelations. Nor was the fulfil- 
ment of that promise long delayed. 
Many opticians, indeed, quite despaired 
of ever being able to make a satisfactory 
refracting compound microscope, and 
some of them had taken up anew Sir Isaac 
Newton’s suggestion in reference to a re- 
flecting microscope. In particular, Pro- 
fessor Giovanni Battista Amici, a very 
famous mathematician and practical opti- 
cian of Modena, succeeded in construct- 
ing a reflecting microscope which was 
said to be superior to any compound mi- 
croscope of the time, though the events 
of the ensuing years were destined to rob 
it of all but historical value. For there 
were others, fortunately, who did not de- 
spair of the possibilities of the refracting 
microscope, and their efforts were des- 
tined before long to be crowned with a 
degree of success not even dreamed of by 
any preceding generation. 
The man to whom chief credit is due 
for directing those final steps that made 
111. 
Indeed, so numerous and so important 
were the discoveries now made in the 
realm of minute anatomy that the rise of 
histology to the rank of an independent 
science may be said to date from this pe- 
riod. Hitherto, ever since the discovery 
of magnifying - glasses, there had been 
here and there a man, sucli as Leuwen- 
hoek or Malpighi, gifted with exception- 
al vision, and perhaps unusually happy 
in his conjectures, who made important 
contributions to the knowledge of the 
minute structure of organic tissues; but 
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 very near the truth 
regarding them, unanimity of opinion was possible 
only after the verdict of the perfected microscope 
was given. 
JEAN BAPTISTE DUMAS. 
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. 
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.” 
CLAUDE BERNARD. 
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 
dealt with it in his work on vegetable physiology, 
WILLIAM BENJAMIN CARPENTER. 
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 from which 
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- 
cleus is so important in the vegetable 
cell as Schleiden believed, the nucleus 
should also be found in the ultimate 
particles of animal tissues. 
HUGO YON SIOHL. 
published not long afterwards; but it re- 
mained for another German, the professor 
of botany in the university of Jena, Dr. 
M. J. Schleiden, to bring the nucleus to 
popular attention, and to assert its all- 
importance in the economy of the cell. 
Schleiden freely acknowledged bis in- 
debtedness to Brown for first knowledge 
of the nucleus, but he soon carried his 
studies of that structure far beyond those 
of its discoverer. He came to believe 
that the nucleus is really the most im- 
portant portion of the cell, in that it is 
the original structure from which the re- 
mainder of the cell is developed. Hence 
he named it the cytoblast. He outlined 
his views in an epochal paper published 
in Muller’s Archives in 1838, under title 
of “ Beitrage zur Phytogenesis.” This 
paper is in itself of value, yet the most 
important outgrowth of Schleiden’s ob- 
servations of the nucleus did not spring 
from his own labors, but from those of a 
friend to whom he mentioned his discov- 
eries the year previous to their publi- 
cation. This friend was Dr. Theodor 
Schwann, professor of physiology in the 
university of Louvain. 
At the moment when these observa- 
tions were communicated to him Schwann 
Schwann’s researches soon showed the 
entire correctness of this assumption. A 
closer study of animal tissues under the 
microscope showed, particularly in the 
case of embryonic tissues, that “opaque 
spots” such as Schleiden described are 
really to be found there in abundance 
—forming, indeed, a most characteristic 
phase of the structure. The location of 
these nuclei at comparatively regular in- 
tervals suggested that they are found in 
definite compartments of the tissue, as 
Schleiden had shown to be the case with 
vegetables; indeed, the walls that separa- 
ted such cell-like compartments one from 
another were in some cases visible. Par- 
ticularly was this found to be the case 
with embryonic tissues, and the study of 
these soon convinced Schwann that his 
original surmise had been correct, and 
that all animal tissues are in their incipi- 
ency composed of particles not unlike the 
ultimate particles of vegetables—in short, 
of what the botanists termed cells. Adopt- 
ing this name, Schwann propounded what 
soon became famous as his cell theory, 
under title of Mikroskopische Untersu- 
chungen iiber die Uebereinstimmung in 
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 the wall itself. This, 
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 
grow so rapidly as to dissociate itself from 
its contents, thus becoming a hollow bub- 
ble or true cell; but the nucleus, as long 
as it lasted, was supposed to continue in 
contact with the cell wall. Schleiden had 
even supposed the nucleus to be a con- 
stituent part of the wall, sometimes lying 
enclosed between two layers of its sub- 
stance, and Schwann quoted this view 
with seeming approval. Schwann be- 
lieved, however, that in the mature cell 
the nucleus ceased to be functional, and 
disappeared. 
JOHANNES MULLER. 
Dumortier, Purkinje, and Muller, all of 
whom Schwann himself had quoted. 
Moreover, there were various physiolo- 
gists who earlier than any of these had 
foreshadowed the cell theory; notably 
Kaspar Friedrich Wolff toward the close 
of the previous century, and Treviranus 
about 1807. But, as we have seen in so 
many other departments of science, it is 
one thing to foreshadow a discovery, it 
is quite another to give it full expression 
and make it germinal of other discov- 
eries. And when Schwann put forward 
the explicit claim that “there is one uni- 
versal principle of development for the 
elementary parts of organisms, however 
different, and this principle is the for- 
mation of cells,” he enunciated a doc- 
trine which was for all practical purposes 
absolutely new, and opened up a novel 
field for the microscopists to enter. A 
most important era in physiology dates 
from the publication of his book in 1889. 
The main thesis as to the similarity of 
development of vegetable and animal 
tissues, and the cellular nature of the ul- 
timate constitution of both, was supported 
by a mass of carefully gathered evidence 
which a multitude of microscopists at 
once confirmed, so Schwann’s work be- 
came a classic almost from the moment 
of its publication. Of course various 
other workers at once disputed Schwann’s 
claim to priority of discovery, in particu- 
lar the English microscopist Valentin, 
who asserted, not without some show of 
justice, that he was working closely along 
the same lines. But so, for that matter, 
wei*e numerous others, as Henle, Turpin, 
IY. 
That Schwann should have gone to 
embryonic tissues for the establishment 
of his ideas was no doubt due very large- 
ly to the influence of the great Russian 
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 
von Mold, professor of 
MAX SCHULTZE. 
botany in tbe universi- 
ty of Tubingen, in the course of his ex- 
haustive studies of the vegetable cell, was 
impressed with the peculiar and charac- 
teristic appearance of the cell contents. 
He observed universally within the cell 
“ an opaque, viscid fluid, having granules 
intermingled in it,” which made up the 
main substance of the cell, and which 
particularly impressed him because under 
certain conditions it could be seen to be 
actively in motion, its parts separated into 
filamentous streams. 
years earlier bad published the first part 
of his celebrated work on embryology, 
and whose ideas were rapidly gaining 
ground, thanks largely to the advocacy 
of a few men, notably Johannes Muller 
in Germany, and William B. Carpenter 
in England, and to the fact that the im- 
proved microscope had made minute an- 
atomy popular. Schwann’s researches 
made it plain that the best field for the 
study of tbe animal cell is here, and a 
host of explorers entered the field. The 
result of their observations was, in the 
main, to confirm the claims of Sch wann 
as to the universal prevalence of the cell. 
The long-current idea that animal tissues 
grow only as a sort of deposit from the 
blood-vessels was now discarded, and the 
fact of so-called plantlike growth of ani- 
mal cells, for which Schwann contended, 
Von Mohl called attention to the fact 
that this motion of the cell contents had 
been observed as long ago as 1774 by 
Bonaventura Corti, and rediscovered in 
1807 by Treviranus, and that these ob- 
servers had described the phenomenon 
under the “most unsuitable name of ‘ro- 
tation of the cell sap.’ ” Von Mohl rec- THE CENTURY’S PROGRESS IN ANATOMY AND PHYSIOLOGY. 
629 
ognized that the streaming substance was 
something quite different from sap. He 
asserted that the nucleus of the cell lies 
within this substance, and not attached 
to the cell wall as Schleiden had contend- 
ed. He saw, too, that the chlorophyl 
granules, and all other of the cell con- 
tents, are incorporated with the “ opaque, 
viscid fluid,” and in 1846 he had become 
so impressed with the importance of this 
universal cell substance that he gave it 
the name of protoplasm. Yet in so doing 
he had no intention of subordinating the 
cell wall. The fact that Payen, in 1844, 
had demonstrated that the cell walls of 
all vegetables, high or low, are composed 
largely of one substance, cellulose, tend- 
ed to strengthen the position of the cell 
wall as the really essential structure, of 
which the protoplasmic contents were 
only subsidiary products. 
vellously similar in appearance and gen- 
eral properties. The closer the observa- 
tion the more striking seemed this simi- 
larity; and finally, about 1860, it was 
demonstrated by Heinrich de Bary and by 
Max Schultze that the two are to all in- 
tents and purposes identical. Even ear- 
lier, Remak had reached a similar con- 
clusion, and applied von Mohl’s word 
protoplasm to animal cell contents, and 
now this application soon became univer- 
sal. Thenceforth this protoplasm was to 
assume the utmost importance in the phy- 
siological world, being recognized as the 
universal “physical basis of life,” veg- 
etable and animal alike. This amounted 
to the logical extension and culmination 
of Schwann’s doctrine as to the similarity 
of development of the two animate king- 
doms. Yet at the same time it was in 
effect the banishment of the cell that 
Schwann had defined. The word cell 
was retained, it is true, but it no longer 
signified a minute cavity. It now im- 
plied, as Schultze defined it, “a small 
mass of protoplasm endowed with the at- 
tributes of life.” This definition was des- 
tined presently to meet with yet another 
modification, as we shall see; but the 
conception of the protoplasmic mass as 
the essential ultimate structure, which 
might or might not surround itself with 
a protective covering, was a permanent 
addition to physiological knowledge. The 
earlier idea had, in effect, declared the 
shell the most important part of the egg; 
this developed view assigned to the yolk 
its true position. 
Meantime, however, the students of an- 
imal histology were more and more im- 
pressed with the seeming preponderance 
of cell contents over cell walls in the tis- 
sues they studied. They too found the 
cell to be filled with a viscid, slimy fluid, 
capable of motion. To this Dujardin 
gave the name of sarcode. Presently it 
came to be known, through the labors of 
Kolliker, Nageli, Bischoff, and various 
others, that there are numerous lower 
forms of animal life which seem to be 
composed of this sarcode, without any 
cell wall whatever. The same thing 
seemed to be true of certain cells of high- 
er organisms, as the blood corpuscles. 
Particularly in the case of cells that 
change their shape markedly, moving 
about in consequence of the streaming of 
xheir sarcode, did it seem certain that no 
cell wall is present; or that, if present, its 
role must he insignificant. 
And so histologists came to question 
whether, after all, the cell contents rather 
than the enclosing wall must not be the 
really essential structure, and the weight 
of increasing observations finally left no 
escape from the conclusion that such is 
really the case. But attention being thus 
focalized on the cell contents, it was at 
once apparent that there is a far closer 
similarity between the ultimate particles 
of vegetables and those of animals than 
had been supposed. Cellulose and ani- 
mal membrane being now regarded as 
mere by-products, the way was clear for 
the recognition of the fact that vegetable 
protoplasm and animal sarcode are mar- 
In one other important regard the the- 
ory of Schleiden and Schwann now be- 
came modified. This referred to the 
origin of the cell. Schwann had regard- 
ed cell growth as a kind of crystalliza- 
tion, beginning with the deposit of a 
nucleus about a granule in the intercel- 
lular substance the cytoblastema, as 
Schleiden called it. But von Mohl, as 
early as 1835, had called attention to the 
formation of new vegetable cells through 
the division of a pre-existing cell. Ehren- 
berg, another high authority of the time, 
contended that no such division occurs, 
and the matter was still in dispute when 
Schleiden came forward with his discov- 
ery of so-called free cell formation with- 
in the parent cell, and this for a long 
time diverted attention from the process 
of division which von Mohl had de- 
scribed. All manner of schemes of cell 
Vol. XCVI.— No. 574.-77 630 
HARPER’S NEW MONTHLY MAGAZINE. 
formation were put forward during the 
ensuing years by a multitude of observ- 
ers, and gained currency notwithstanding 
von Mold’s reiterated contention that 
there are really but two ways in which 
the formation of new cells takes place, 
namely, “ first, through division of older 
cells; secondly, through the formation of 
secondary cells lying free in the cavity of 
a cell.” 
cell, however specialized, ever forget alto- 
gether any one of its primordial func- 
tions or capacities. All physiology, then, 
properly interpreted, becomes merely a 
study of cellular activities; and the de- 
velopment of the cell theory takes its 
place as the great central generalization 
in physiology of our century. Something 
of the later developments of this theory 
we shall see in another connection. 
But gradually the researches of such 
accurate observers as Unger, Nageli, 
Kdlliker, Reichart, and Remak tended to 
confirm the opinion of von Mold that 
cells spring only from cells, and finally 
Rudolf Virchow brought the matter to 
demonstration about 1860. His Omnis 
cellula e cellula became from that time 
one of the accepted data of physiology. 
This was supplemented a little later by 
Fleming’s Omnis nucleus e nucleo, when 
still more refined methods of observation 
had shown that the part of the cell which 
always first undergoes change prepara- 
tory to new cell formation is the all-es- 
sential nucleus. Thus the nucleus was 
I’estored to the important position which 
Schwann and Schleiden had given it, but 
with greatly altered significance. In- 
stead of being a structure generated de 
novo from non - cellular substance, and 
disappearing as soon as its function of 
cell-formation was accomplished, the nu- 
cleus was now known as the central and 
permanent feature of every cell, inde- 
structible while the cell lives; itself the 
division - product of a pre - existing nu- 
cleus, and the parent, by division of its 
substance, of other generations of nuclei. 
The word cell received a final definition 
as “ a small mass of protoplasm supplied 
with a nucleus.” 
Y. 
Just at the time when the microscope 
was opening up the paths that were to 
lead to the wonderful cell theory, another 
novel line of interrogation of the living 
organism was being put forward by a dif- 
ferent set of observers. Two great schools 
of physiological chemistry had arisen 
—one under guidance of Liebig and 
Wohler in Germany, the other dominated 
by the great French master Jean Baptiste 
Dumas. Liebig had at one time contem- 
plated the study of medicine, and Dumas 
had achieved distinction in connection 
with Prevost at Geneva in the field of 
pure physiology before he turned his at- 
tention especially to chemistry. Both 
these masters, therefore, and Wohler as 
well, found absorbing interest in those 
phases of chemistry that have to do with 
the functions of living tissues; and it was 
largely through their efforts and the la- 
bors of their followers that the prevalent 
idea that vital processes are dominated by 
unique laws was discarded and physiology 
was brought within the recognized prov- 
ince of the chemist. So at about the 
time when the microscope had taught 
that the cell is the really essential struc- 
ture of the living organism, the chemists 
had come to understand that every func- 
tion of the organism is really the expres- 
sion of a chemical change—that each cell 
is, in short, a miniature chemical labora- 
tory. And it was this combined point of 
view of anatomist and chemist, this union 
of hitherto dissociated forces, that made 
possible the inroads into the unexplored 
fields of physiology that were effected 
toward the middle of our century. 
One of the first subjects reinvestigated 
and brought to proximal solution was the 
long-mooted question of the digestion of 
foods. Spallanzani and Hunter had shown 
in the previous century that digestion is 
in some sort a solution of foods; but lit- 
tle advance was made upon their work 
until 1824, when Prout detected the pres- 
In this widened and culminating gen- 
eral view of the cell theory it became 
clear that every animate organism, ani- 
mal or vegetable, is but a cluster of nu- 
cleated cells, all of which, in each indi- 
vidual case, are the direct descendants of 
a single primordial cell of the ovum. In 
the developed individuals of higher or- 
ganisms the successive generations of 
cells become marvellously diversified in 
form and in specific functions; there is a 
wonderful division of labor, special func- 
tions being chiefly relegated to definite 
groups of cells; but from first to last there 
is no function developed that is not pres- 
ent, in a primitive way, in every cell, 
however isolated; nor does the developed THE CENTURY’S PROGRESS IN ANATOMY AND PHYSIOLOGY. 
631 
ence of hydrochloric acid in the gastric 
juice. A decade later Sprott and Boyd 
detected the existence of peculiar glands 
in the gastric mucous membrane; and 
Cagniard ia Tour and Schwann indepen- 
dently discovered that the really active 
principle of the gastric juice is a sub- 
stance which was named pepsin, and 
which was shown by Schwann to be ac- 
tive in the presence of hydrochloric acid. 
Almost coincidently, in 1836, it was dis- 
covered by Purkinje and Pappenheim 
that another organ than the stomach—the 
pancreas, namely—has a share in diges- 
tion, and in the course of the ensuing 
decade it came to be known, through the 
efforts of Eberle, Valentin, and Claude 
Bernard, that this organ is all-important 
in the digestion of starchy and fatty foods. 
It was foundytoo, that the liver and the 
intestinal glands have each an important 
share in the work of preparing foods for 
absorption, as also has the saliva—that, 
in short, a coalition of forces is necessary 
for the digestion of all ordinary foods 
taken into the stomach. 
off during respiration the chemists of the 
age of Priestley and Lavoisier had in- 
deed made clear, but the mistaken notion 
prevailed that it was in the lungs them- 
selves that the important burning of fuel 
occurs, of which carbonic acid is a chief 
product. But now that attention had 
been called to the importance of the 
ultimate cell, this misconception could 
not long hold its ground, and as early 
as 1842, Liebig, in the course of his stud- 
ies of animal heat, became convinced that 
it is not in the lungs, but in the ultimate 
tissues to which they are tributai*y, that 
the true consumption of fuel takes place. 
Reviving Lavoisier’s idea, with modifica- 
tions and additions, Liebig contended, 
and in the face of opposition finally de- 
monstrated, that the soui’ce of animal heat 
is really the consumption of the fuel 
taken in through the stomach and the 
lungs. He showed that all the activities 
of life are really the product of energy 
liberated solely through destructive pro- 
cesses, amounting, broadly speaking, to 
combustion occurring in the ultimate 
cells of the organism. 
And the chemists soon discovered that 
in each one of the essential digestive 
juices there is at least one substance hav- 
ing certain resemblances to pepsin,though 
acting on different kinds of food. The 
point of resemblance between all these 
essential digestive agents is that each has 
the remarkable property of acting on 
relatively enormous quantities of the sub- 
stance which it can digest without itself 
being destroyed or apparently even al- 
tered. In virtue of this strange property, 
pepsin and the allied substances were 
spoken of as ferments, but more recently 
it is customary to distinguish them from 
such organized ferments as yeast by desig- 
nating them enzymes. The isolation of 
these enzymes, and an appreciation of their 
mode of action, mark a long step toward 
the solution of the riddle of digestion, 
but it must be added that we are still 
quite in the dark as to the real ultimate 
nature of their strange activity. 
Further researches showed that the 
carriers of oxygen, from the time of its 
absorption in the lungs till its liberation 
in the ultimate tissues, are the red cor- 
puscles, whose function had been supposed 
to be the mechanical one of mixing of 
the blood. It transpired that the red 
corpuscles are composed chiefly of a sub- 
stance which Kiihne first isolated in crys- 
talline form in 1865, and which was named 
haemoglobin—a substance which has a 
marvellous affinity for oxygen, seizing 
on it eagerly at the lungs, yet giving it 
up with equal readiness when coursing 
among the remote cells of the body. 
When freighted with oxygen it becomes 
oxyhasmoglobin, and is red in color; 
when freed from its oxygen it takes a 
purple hue; hence the widely different 
appearance of arterial and venous blood, 
which so puzzled the early physiologists. 
This proof of the vitally important role 
played by the red blood corpuscles led, 
naturally, to renewed studies of these in- 
finitesimal bodies. It was found that they 
may vary greatly in number at diffei’ent 
periods in the life of the same individual, 
proving that they may be both developed 
and destroyed in the adult organism. In- 
deed, extended observations left no rea- 
son to doubt that the process of corpuscle 
formation and destruction may be a per- 
In a comprehensive view, the digestive 
organs, taken as a whole, are a gateway 
between the outside world and the more 
intimate cells of the organism. Another 
equally important gateway is furnished 
by the lungs, and here also there was 
much obscurity about the exact method 
of functioning at the time of the revival 
of physiological chemistry. That oxy- 
gen is consumed and carbonic acid given 633 
HARPER’S NEW MONTHLY MAGAZINE. 
fectly normal one; that, in short, every 
red blood corpuscle runs its course and 
dies like any more elaborate organism. 
They are'formed constantly in the red 
marrow of bones, and are destroyed in 
the liver, where they contribute to the 
formation of the coloring matter of the 
bile. Whether there are other seats of 
such manufacture and destruction of the 
corpuscles is not yet fully determined. 
Nor are histologists agreed as to whether 
the red blood corpuscles themselves are 
to be regarded as true cells, or merely as 
fragments of cells budded out from a true 
cell for a special purpose; but, in either 
case, there is not the slightest doubt that 
the chief function of the red corpuscle is 
to carry oxygen. 
a ductless organ, but the quantity of its 
biliary output seems utterly dispropor- 
tionate to its enormous size, particularly 
when it is considered that in the case of 
the human species the liver contains nor- 
mally about one-fifth of all the blood in 
the entire body. Bernard discovered that 
the blood undergoes a change of composi- 
tion in passing through the liver. The 
liver cells (the peculiar forms of which 
had been described by Purkiuje, Henle. 
and Dutrochet about 1838) have the power 
to convert certain of the substances that 
come to them into a starchlike com- 
pound called glycogen, and to store this 
substance away till it is needed by the 
organism. This capacity of the liver 
cells is quite independent of the bile- 
making power of the same cells; hence 
the discovery of this glycogenic function 
showed that an organ may have more 
than one pronounced and important spe- 
cific function. But its chief importance 
was in giving a clew to those intermedi- 
ate processes between digestion and final 
assimilation that are now known to be of 
such vital significance in the economy of 
the organism. 
If the oxygen is taken to the ultimate 
cells before combining with the combus- 
tibles it is to consume, it goes without 
saying that these combustibles themselves 
must be carried there also. Nor could it 
be in doubt that the chiefest of these ul- 
timate tissues, as regards quantity of fuel 
required, are the muscles. A general and 
comprehensive view of the organism in- 
cludes, then, digestive apparatus and lungs 
as the channels of fuel-supply; blood 
and lymph channels as the transporta- 
tion system; and muscle cells, united into 
muscle fibres, as the consumption fur- 
naces, where fuel is burned and energy 
transformed and rendered available for 
the purposes of the organism, supple- 
mented by a set of excretory organs, 
through which the waste products—the 
ashes—are eliminated from the system. 
In the forty-odd years that have elapsed 
since this pioneer observation of Bernard, 
numerous facts have come to light show- 
ing the extreme importance of such inter- 
mediate alterations of food-supplies in the 
blood as that performed by the liver. It 
has been shown that the pancreas, the 
spleen, the thyroid gland, the suprarenal 
capsules, each in its own way, are absolute- 
ly essential to the health of the organism, 
through metabolic changes which they 
alone seem capable of performing; and 
it is suspected that various other tissues, 
including even the muscles themselves, 
have somewhat similar metabolic capaci- 
ties in addition to their recognized func- 
tions. But so extremely intricate is the 
chemistry of the substances involved that 
in no single case has the exact nature of 
the metabolisms wrought by these organs 
been fully made out. Each is in its way 
a chemical laboratory indispensable to 
the right conduct of the organism, but 
the precise nature of its operations re- 
mains inscrutable. The vast importance 
of the operations of these intermediate 
organs is unquestioned. 
But there remain, broadly speaking, 
two other sets of organs whose size de- 
monstrates their importance in the econo- 
my of the organism, yet whose functions 
are not accounted for in this synopsis. 
These are those glandlike organs, such 
as the spleen, which have no duct and 
produce no visible secretions; and the 
nervous mechanism, whose central organs 
are the brain and spinal cord. What of- 
fices do these sets of organs perform in 
the great labor-specializing aggregation 
of cells which we call a living organism? 
As regards the ductless glands, the first 
clew to their function was given when 
the great Frenchman Claude Bernard 
(the man of whom his admirers loved to 
say, “he is not a physiologist merely; he 
is physiology itself ”) discovered what is 
spoken of as the glycogenic function of 
the liver. The liver itself, indeed, is not 
A consideration of the functions of that 
other set of organs known collectively 
as the nervous system is reserved for a 
later paper. fa & _ 
JBk it Iplm 
M l||l 
'■•• •.• . '■. > . ..- .. . ..-•: :■■;:< . ~ 
No. 574. 
MARCH, 1898. 
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