( Originally Published 1913 )
To the analysis of the fundamental statical condition of living beings, succeeds the co-ordination of all known organisms into one hierarchy ; in other words, to Anatomy succeeds zoological Classification. The chap-ter devoted to this subject by Comte is full of interest, but I must pass it over with a mere indication. He decides against Lamarck's celebrated development hypo-thesis. Although his admiration of Lamarck, and appreciation of his influence on philosophical zoology, is such as may be expected from so great and liberal a thinker, he does not, as it appears to me, fully appreciate the immense value of this hypothesis if merely treated as a philosophic artifice, let its truth be what it may.
Having set down the general consideration necessary as a prelude to classification, Comte commences his survey of the dynamical conditions of Biology; or what in common parlance is termed Physiology, as distinguished from Anatomy.
Physiology first demands a fundamental division into Vegetative Life and Animal Life, corresponding not only with the two kingdoms Vegetable and Animal, but with the twofold life of every animal—viz., the organic life and the relative life. The Vegetative, as more simple, more general, and first in the order of time, demands priority in study ; the animal depends upon the vegetable, the vegetable does not depend upon the animal. Now in the phenomena of Vegetative Life we see very distinctly the co-operation of all those laws of inorganic matter which the previous sciences have made us acquainted with; and Comte has sketched what he calls " the theory of media," or indispensable circumstances, as a necessary preliminary* to this part of the science.
" The true philosophic character of physiology consists in the institution of an exact and constant harmony between the static and dynamic points of view, between the ideas of organization and the ideas of life, between the notion of agent and that of act; hence results the necessity of reducing all our abstract conceptions of physiological properties to the consideration of elementary and general phenomena, every one of which necessarily recalls to our mind the idea of a locality more or less circumscribed. One may say, in short, that the reduction of the various functions to cor-responding properties must be regarded as the consequence of the habitual analysis of life itself into its different functions, setting aside all vain pretensions to discover causes, and bearing in view only the discovery of laws. Otherwise, the ideas of properties will fall back into the ancient notions of metaphysical entities.
" In endeavouring to make our different degrees of physiological analysis correspond with those of anatomical analysis, we may begin by saying that the idea of property, which lies at the bottom of the one, must correspond with that of tissue, which lies at the bottom of the other; while the idea of function corresponds with that of organ : so that the successive notions of function and property present a gradation perfectly similar to that which exists between the notions of organ and tissue."
It has already been seen, in treating of the tissues, that we must divide them into, 1st, one primordial generative tissue—the cellular ; and 2nd, the secondary and special tissues which result from the combination of certain substances with this primary tissue. That is to say, there is the cellular tissue and its modifications; and there is the combination of this tissue with fibrin and neurine to form muscular and nervous tissues. The physiological properties must therefore be divided into correspondent classes—1st, those general properties which belong to all the tissues, and which constitute the life, so to speak, of the primordial cellular tissue; and 2nd, those special properties which characterize the most distinctive modifications—i. e., the muscular and nervous tissues. Thus we return to the great fundamental distinction between Vegetative and Animal Life.
" If," says Comte, " we consider the condition of opinion with reference to this matter, we shall find, that, as regards the two special secondary tissues, very clear and important conclusions have been obtained of their properties, because in accordance with the natural march of intelligence, the most striking phenomena are the soonest appreciated. All the general phenomena of animal life are, now-a-days, unanimously connected with contractility and sensibility, considered each as the characteristic attribute of a distinct tissue. But there reigns extreme confusion and difference with regard to the general properties of vegetative life."
The two capital functions of Vegetative Life are those which, in their constant connection and antagonism, correspond with the definition of Life itself :
1st. Absorption, internally, of those materials drawn from the surrounding medium, which, after their gradual assimilation, result in what we call nutrition or growth.
2nd. Exhalation, externally, of those molecules which are not assimilated, or are produced by disassimilation in the waste of tissues.
No other fundamental notion enters the idea of Life, if we separate from it, as we ought, all ideas relative to animal life, which, as a more special modification, does not affect the general problem.
" In no organism can the assimilable materials be directly incorporated, either at the place of absorption or under their primitive form ; their assimilation requires a certain displacement, and a preparation accomplished during the passage. It is the same, inversely, with exhalation, which presupposes that the particles which have become useless to a certain portion of the organism, are finally exhaled from another portion, after having undergone, in the passage, certain indispensable modifications. In this respect, as in so many others, it seems to me that great exaggeration has been made of the distinction between the animal and vegetable organism, the more, especially when it has been attempted to make digestion an essential character of animality. For, in forming the most general notion of digestion, which must extend to all preparation of aliments indispensable to their assimilation, it is quite clear that this preparation exists in the vegetable as well as in the animal, although less profound and varied, in consequence of the simplicity of the aliments and of the organism. The same remark applies to the movement of the fluids."
To these functions of Absorption and Exhalation (between which we must necessarily interpose Assimilation, as the result of absorption), we must add a fourth, which, issuing out of Assimilation, presents three great aspects : Growth, Generation, Death ;—all dependent upon cell multiplication, and varying according to a law I hope some day to demonstrate, with the aid of my friend Herbert Spencer's discovery, succinctly expressed by him in the formula, individuation is antagonistic to reproduction.
It may be well here to state one of the fundamental laws of assimilation, which we owe, I believe, to Chevreul :
There is an intimate relation between the chemical composition of an aliment and the organism which it nourishes.
A plant or an animal may be nourished in two ways: 1st, when attached to the parent as seed or embryo; 2nd, when separated from the parent and drawing its food from the surrounding medium. On analysing the proximate principles contained in the seed or egg, we find them belonging to the principal types subsequently found in the developed being. And if in passing from oviparous to mammiferous animals--we examine the young animal in reference to the milk which for a long while forms its entire nourishment, we find a perfect correspondence between the aliment and the- structure. The proximate principles of milk are " fitted to combine molecule to molecule with the principles—exactly cor-responding or analogous—already existing in the organs they are to nourish."
If we consider the plant separated from its parent and the animal separated from its parent, we detect at once a capital distinction in their power of assimilating substance from the external world. 'The plant, simpler in its organization, is able to assimilate water and gas ; on the other hand, the manure necessary for its complete development presents organic matters, more or less altered at the moment of entrance.
In passing from the plant to the animal, we observe that the more complex the organization the more complex are the aliments which nourish it, and the more analogous are their proximate principles to the principles of the organs they sustain. Thus we see that plants are nourished by water, carbonic acid, and other gases and organic matters (in the shape of manure, that is to say, reduced to simpler and more soluble principles); on the contrary, animals more complex and more elevated in the organic scale need matters more complex in proximate principles, and consequently more varied in properties.
A slight modification of the foregoing statement is necessary, and one which leads me to correct an error almost if not quite universal; the error, namely, of supposing that Animals are distinguished from Plants by their inability to nourish themselves directly with the materials furnished by the external world. That Plants can convert inorganic substances into their own substance, but that Animals have no such power—requiring the intervention of plants for that purpose,—is a proposition to be met with as beyond a doubt in every book on physiology.
The proposition is erroneous; it is too absolute. The portion of truth it contains is this : animals cannot nourish themselves solely by materials taken directly from the inorganic world, in the way plants nourish themselves by the air, water, and alkalies directly furnished them.
But does this mean more than that complex structures, by reason of their complexity, cannot be built up in the same way as the simple ? If animals were nourished in the same way and on the same materials as plants, we, should not find such immense differences between them.
Ordinary experience is sufficient to show—when once the idea is started, and the old assumption which men have received unquestioned, is questioned—that animals, besides converting organic substances into their own tissue, do also convert inorganic substances into their own tissue with a precision and an abundance scarcely surpassed by plants. They take the oxygen directly from the air to vitalize their blood ; they take the water directly from the spring ; they take salts in their food and out of it ; they take up iron, and various mineral substances, indirectly, if you will, i. e., in their food ; but, nevertheless, if you deprive the food of its inorganic substances the animal will perish. Nay, we see by the example of Birds that chalk is necessary to life. In Al. Chossat's experiments, pigeons were deprived of all chalky substances not actually in the corn he fed them with. At first they fattened and grew heavier. At the end of three months they augmented their quantity of drink—as much as eight times their previous quantity. They suffered from diarrhoea par insuffisance de principes calcaires. Finally, they died, being utterly unable to sustain life without a certain amount of chalk !
Every physiologist knows the large proportion of in-organic substances in the organic tissues especially water and phosphate of lime. Water forms nearly eighty per cent. of our bodies; and there is no evidence that any portion of this water is formed in the body.
We have only to consider what the Law of Assimilation is, to see at once the real nature of the proposition respecting Animals and Plants. The Law of Assimilation depending on the chemical relation between aliment and structure, it follows that the more complex the structure the more complex must be the food : hence the' reason why Animals cannot nourish themselves solely with the aliment which suffices for the simpler structures of Plants.
The gradation is as follows :—The simplest plants need only anorganic substances ; the higher plants need those substances, and also certain merorganic substances, the débris of organic matter—manure. of The lower animals need anorganic, merorganic, and teleorganic substances—air, water, salts, plants, &c. The higher animals also need these, but in different proportions—with greater preponderance of the teleorganic in pro-portion as the organization of the animal is more complex—(Herbivora, Carnivora). So that we must modify Comte's definition of animals, " organized beings nourished by matters which have once lived," as distinguished from Plants, " organized beings nourished by matters which have not lived," and insert the word mainly into the definition.
Following out this Law of Assimilation, we see the reason of the results obtained by Magendie, viz., that no organic substance will by itself suffice for aliment; nor, indeed, will all the organic substances together suffice if deprived of the other proximate principles, i. e. the inorganic. It is obvious that the body, which is composed of three classes of principles, cannot be nourished by an aliment containing only one of these. Hence the fallacy of Liebig's celebrated argument respecting the non-nutritive properties of gelatine—an argument moreover in direct contradiction with the principles he has himself laid down; gelatine alone is not nutritive, nor is albumen alone, nor fat alone, nor salts alone.
Finally, it is owing to the relation between Aliment and Structure that the organism separates the food into two portions, one of which it absorbs into its interior, the other it rejects as unfit for use. And we trace the operation of the same law in the formation of the special tissues. The blood is the blastema from which one and all select their nourishment ; but each selects that only which bears the due relation to it.