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undertake now what was before impossible-an exact enumeration of anatomical elements. And again, these tissues can be classified according to their true general relations; and may even be reduced to a single tissue, modified by determinate laws. These two are the other chief transformations undergone by the great anatomical theory of Bichat, through the application of the comparative method and these two we now proceed to review.

The first is connected with the great question of the vitality of the organic fluids, about Vitality of the organic fluids. which our ideas are far from being, I think, sufficiently settled. Every living body consists of a combination of solids and fluids, the respective proportions of which vary, according to the species, within very wide limits. The very definition of the vital state supposes this conjunction; for the double motion of composition and decomposition which characterizes life could not take place among solids alone; and, on the other hand, a liquid or gaseous mass not only requires a solid envelope, but could admit of no real organization. If the two great primitive ideas of Life and Organization were not inseparable, we might imagine the first to belong to fluids, because they are so readily modified; and the other to solids, as alone capable of structural formation: and here, under another view, we should find the necessary harmony of the two elements. The comparison of types in the biological series. confirms, in fact, the general rule that the vital activity increases with the preponderance of fluid elements in the organism; while a greater persistence of the vital state attends the preponderance of solids. This has long been regarded as a settled law by philosophical biologists, in studying the series of ages alone. These considerations seem to show that the controversy about the vitality of fluids rests, like many other famous controversies, on a vicious proposal of the problem, since such a mutual relation of the solids and the fluids excludes at once both humourism and solidism. Discarding, of course, the products from the question, there can be no doubt that the fluid elements of the organism manifest a life as real as that of the solids. The founders of modern pathology, in their reaction against the old humourism, have not paid

sufficient attention, in the theory of diseases, to the direct and spontaneous alterations of which the organic fluids, especially the blood, are remarkably susceptible, in virtue of the complexity of their composition. It would appear, from a philosophical point of view, very strange if the most active and susceptible of the anatomical elements did not participate, primarily or consecutively, in the perturbations of the organism. But, on the other hand, it is not less certain that the fluids, animal and vegetable, cease to live as soon as they have quitted the organism; as, for instance, the blood after venesection. They then lose all organization, and are in the condition of products. The vitality of the fluids, considered separately, constitutes them an illdefined, and therefore interminable, question.

A truly positive inquiry however arises out of the question-the inquiry as to which of the immediate principles of a fluid are vital; for it cannot be admitted that all are so indiscriminately. Thus, the blood being chiefly composed of water, it would be absurd to suppose such an inert vehicle to participate in the life of the fluid; but then, which of the other constituents is the seat of life? Microscopic anatomy gives us the answer,—that it resides in the globules, properly so called, which are at once organized and living. However valuable such a solution would be, it can be regarded at present only as an attempt; for it is admitted that these globules, though determinate in form, shrink more and more as the arterial blood passes through an inferior order of vessels, that is, as it approaches its incorporation with the tissues; and that, at the precise moment of assimilation, there is a complete liquefaction of the globules. It would thus appear that we must cease to regard the blood as living at the very moment when it accomplishes its chief act of vitality. Before any decision can be made, we must have the counter proof,—the acknowledgment that true globules are exclusively characteristic of living fluids, in opposition to those which, as simple products, are essentially inert, and hold in suspension various solids, which make them difficult to be distinguished from true globules, notwithstanding the determinate form of the latter. Microscopical observations are too delicate, and sometimes deceptive, to admit at pre

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sent of the irreversible establishment of this essential point of anatomical doctrine.

The statical study of living bodies would form but a very incomplete introduction to the dynamical, if the fluids were left out of the investigation of the organic elements, however much remains to be desired in our knowledge of them. The omission of them in Bichat's treatise leaves a great gap. Still, as the anatomy of solids must always take precedence of that of fluids, Bichat chose the true point of departure, though he did not undertake the whole subject. It must be added that the examination of the fluids is so much the more difficult of the two as to be wellnigh impracticable. In an anatomical sense, it is impracticable: and the two only methods,-microscopical and chemical examination, are impaired by the rapid disorganization which ensues when the fluids quit the organism. The chemical method is in itself the more valuable of the two : but, besides that the chemists habitually confound the elements and the products, they have always examined the former in a more or less advanced state of decomposition: and, being unaware of this, they have offered only the most false and incoherent notions of the molecular constitution of the organized fluids. In such a state of things, it is only by a full preparation, from the study of the solid elements, that anything can be done in the study of the fluids. It is almost needless to say that by the same rule which prescribes this order, we should study fluids in the order of their increasing liquefaction,-taking the fatty substances first, then the blood and other liquids, and lastly the vaporous and gaseous elements, which will always be the least understood.

The order of inquiry being thus settled, Classification the next subject is the rational classification of the tissues. of the tissues, according to their anatomical

filiation. It was not by such a study as Bichat's,—of Man alone, that anything certain could become known of such obscure differences as those of the fundamental tissues. In order to obtain such knowledge the study of the whole biological series is indispensable.

The first piece of knowledge thus obtained is that the cellular tissue is the

ORGANIC.

Cellular tissue.

primitive and essential web of every organism; it being the only one that is present through the whole range of the scale. The tissues which appear in Man so multiplied and distinct lose all their characteristic attributes as we descend the series, and tend to merge entirely in the general cellular tissue, which remains the sole basis of vegetable, and perhaps of the lowest animal organization. This fact harmonizes well with the philosophical account of the basis of life, in its last degree of simplicity; for the cellular tissue is eminently fitted, by its structure, for absorption and exhalation. At the lower end of the series, the living organism, placed in an unvarying medium, does nothing but absorb and exhale by its two surfaces, between which are ever oscillating the fluids destined for assimilation, and those which result from the contrary proFor so simple a function as this the cellular tissue suffices. It remained to be ascertained under what laws the original tissue becomes gradually modified so as to engender all the others, with those attributes which at first disguise their common derivation: and this is what Comparative anatomy has begun to establish, with some distinctness.

cess.

The characteristic modifications of the tissue are of two prominent classes: the first, more common and less profound, are limited to the simple structure: the other class, more special, and more profound, affect the composition itself.

Of the first order the prominent case is that of the dermous tissue, properly so called, which is Dermous the basis of the general organic envelope, extissue. terior and interior. The modification here is mere condensation, differently marked, in regard to animal organisms, according as the surface is, as in exterior surfaces, more exhalant than absorbent, or, as in interior surfaces, more absorbent than exhalant. Even this first transformation is not rigorously universal; and we must ascend the scale a little way to find it clearly characterized. Not only in some of the lowest of the animal organisms, are the exterior and interior essentially alike, so that the two surfaces may be interchanged, but, if we go a little lower, we find no anatomical distinction between the en

velope and the whole of the organism, which is uniformly cellular.

By an increasing condensation of the parent tissue, three distinct but inseparable tissues proceed from the derma, all of which are destined to an important, though passive office in the animal economy, either as envelopes protecting the nervous organs, or as auxiliaries of the locomotive apparatus. These are the fibrous, cartilaginous, and bony tissues, ranged by Bichat in their rational order, and named by M. Laurent, in their combination, Sclerous tissue. the sclerous tissue. The different degrees of consolidation here arise from the deposition in the cellular network of a heterogeneous substance, organic or inorganic, the extraction of which leaves no doubt as to the nature of the tissue. When, on the other hand, by a last direct condensation, the original tissue becomes itself more compact, without being incrusted by a foreign substance, we recognize a new modification, in which impermeability becomes compatible with suppleness, which is the characteristic of the serous, or (as M. Laurent calls it) the Kystous tissue. kystous tissue, the office of which is to interpose between the various mobile organs, and to contain liquids, both circulating and stagnant.

The second order of transformations ex- ANIMAL. hibits two secondary kinds of tissue which Muscular and distinguish the animal organism, and which nervous tissues. appear at about the same degree of the scale-the muscular and the nervous tissues. In each there is an anatomical combination of the fundamental tissue with a special organic element, semi-solid and eminently vital, which, having long gone by the name of fibrine in the first case, has suggested the corresponding name of neurine (given us by M. de Blainville) for the other. Here the transformation of the parent tissue is so complete, that it would be difficult to establish, and yet more to detect it in the higher organisms; but the analogies of comparative anatomy leave no doubt, and only make us wish that we could understand with more precision the mode of anatomical union of the muscular and nervous substances with the cellular tissue.

Passing on to the chief subdivision of each of the