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Condition of
Dynamical
Biology.

CHAPTER IV.

ORGANIC OR VEGETATIVE LIFE.

E have to pass on to dynamical biology, which is very far indeed from having attained the clearness and certainty of the statical department of the science. Important as are the physiological researches of recent times, they are only preliminary attempts, which must be soundly systematized before they can constitute a true dynamical biology. The minds which are devoted to mathematical, astronomical, and physical studies are not of a different make from those of physiologists; and the sobriety of the former classes, and the extravagance of the latter, must be ascribed to the definite constitution of the simpler sciences and the chaotic state of physiology. The melancholy condition of this last is doubtless owing in part to the vicious education of those who cultivate it, and who go straight to the study of the most complex phenomena without having prepared their understandings by the practice of the most simple and positive speculation: but I consider the prevalent license as due yet more to the indeterminate condition of the spirit of physiological science. In fact, the two disadvantages are one; for if the true character of the science were established, the preparatory education would immediately be rectified.

This infantine state of physiology prescribes the method of treating it here. I cannot proceed, as in statical biology, to an analytical estimate of established conceptions. I can only examine, in pure physiology, the notions of method; that is, the mode of organization of the researches necessary to the ascertainment of the laws of vital phenomena. The progress of biological philosophy depends on the distinct and rational institution of physiological questions, and not on attempts, which must be premature, to resolve

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them. Conceptions relating to method are always important in proportion to the complexity of the phenomena in view: therefore are they especially valuable in the case of vital phenomena; and above all, while the science is in a nascent state.

Vital pheno

mena: their division.

This dis

Though all vital phenomena are truly interconnected, we must, as usual, decompose them, for purposes of speculative study, into those of greater and those of less generality. tinction answers to Bichat's division into the organic or vegetative life, which is the common basis of existence of all living bodies; and animal life, proper to animals, but the chief characters of which are clearly marked only in the higher part of the zoological scale. But, since Gall's time, it has become necessary to add a third division, the positive study of the intellectual and moral phenomena which are distinguished from the preceding by a yet more marked speciality, as the organisms which rank nearest to Man are the only ones which admit of their direct exploration. Though, under a rigorous definition, this last class of functions may doubtless be implicitly included in what we call the animal life, yet its restricted generality, the dawning positivity of its systematic study, and the peculiar nature of the higher difficulties that it offers, all indicate that we ought, at least for the present, to regard this new scientific theory as a last fundamental branch of physiology; in order that an unseasonable fusion should not disguise its high importance, and alter its true character. These, then, are the three divisions which remain for us to study, in our survey of biological science.

Theory of Organic Media,

Before proceeding to the analysis of organic or vegetative life, I must say a few words on the theory of organic media, without considering which, there can be no true analysis of vital phenomena.

This new element may be said to have been practically introduced into the science by that controversy of Lamarck, already treated of, about the variation of animal species through the prolonged influence of external circumstances. It is our business here to exclude from the researches thus introduced, everything but what concerns physiology pro

perly so called, reduced to the abstract theory of the living organism. We have seen that the vital state supposes the necessary and permanent concurrence of a certain aggregate of external actions with the action of the organism itself it is the exact analysis of these conditions of existence which is the object of the preliminary theory of organic media; and I think it should be effected by considering separately each of the fundamental influences under which the general phenomenon of life occurs. It cannot be necessary to point out the importance of the study of this half of the dualism which is the condition of life: but I may just remark on the evidence it affords of the subordination of the organic to the inorganic philosophy; the influence of the medium on the organism being an impracticable study as long as the constitution of the medium is not exactly known.

Exterior con

The exterior conditions of the life of the ditions of Life. organism are of two classes,-physical and chemical; or, in other words, mechanical and molecular. Both are indispensable; but the first may be considered, from their more rigorous and sensible permanence, the most general,-if not as to the different organisms, at least as to the continued duration of each of them.

Mechanical First in generality we must rank the action conditions. of Weight. There is no denying that Man Weight. himself must obey, whether as weight or projectile, the same mechanical laws that govern every other equivalent mass: and by reason of the universality of these laws, weight participates largely in the production of vital phenomena, to which it is sometimes favourable, sometimes opposed, and scarcely ever indifferent. There is great difficulty in the analysis of its effects, because its influence cannot be suspended or much modified for the purpose; but we have ascertained something of them, both in the normal and the pathological states of the organism. In the lower, the vegetable portion of the scale, the physiological action of weight is less varied but more preponderant, the vital state being there extremely simple and least removed from the inorganic condition. The laws and limits of the growth of vegetables appear to depend

EXTERNAL CONDITIONS OF LIFE.

81

essentially on this influence, as is proved by Mr. Knight's experiments on germination, as modified by a quicker or slower motion of rotation. Much higher organisms are subject to analogous conditions, without which we could. not explain, for instance, why the largest animal masses live constantly in a fluid sufficiently dense to support almost their whole weight, and often to raise it spontaneously. However, the superior part of the animal series is least fit for the ascertainment of the physiological influence of weight, from its concurrence with a great number of heterogeneous actions: but this again enables us to study it in a variety of vital operations: for there is scarcely a function, organic, animal, or even intellectual, in which we may not point out the indispensable intervention of weight, which specially manifests itself in all that relates to the stagnation or movement of fluids. It is therefore much to be regretted that a subject so extended and important has not been studied in a rational spirit and method.

Pressure.

The next mechanical condition,-pressure, liquid or gaseous,-is an indirect consequence of weight. Some few scientific results have here been obtained, from the facility with which pressure may be modified by artificial or natural circumstances. There are limits in the barometrical scale, outside of which no atmospherical animal,-Man or any other, can exist. We cannot so directly verify such a law in the case of aquatic animals: but it would seem that in proportion to the density of the medium must be the narrowness of the vertical limits assignable to the abode of each species. Of the relation between these intervals and the degree of organization, it must be owned, however, that we have no scientific knowledge, our ideas being, in fact, wholly confused as to the inferior organisms, and especially in the vegetable kingdom. Though, through many difficulties and complexities, the science is in a merely nascent state, some inquiries, such as those relating to the influence of atmospheric pressure on the venous circulation, and recent observations on its co-operation in the mechanism of standing and moving, etc., show that biologists are disposed to study this order of questions in a rational manner.

Motion and rest.

vestigated.

Among the physical conditions, and perhaps first among them, the physiological influence of motion and rest should be inAmidst the confusion and obscurity which exist on this subject, I think we may conclude that no organism, even the very simplest, could live in a state of complete immobility. The double movement of the earth, and especially its rotation, may probably be as necessary to the development of life as to the periodical distribution of heat and light. Too much care, however, cannot be taken to avoid confounding the motion produced by the organism itself with that by which it is affected from without; and the analysis had therefore better be applied to communicated than spontaneous motion. And as rotary motion tends, by the laws of mechanics, to disorganize any system, and therefore, eminently, to trouble its interior phenomena, it is this kind of motion which may be studied with the best result; for which object we should do well to investigate, in a comparative way, the modifications undergone by the principal functions from the organism being made to rotate in such a gradual variety as is compatible with a normal state. The attempt has as yet been made only with plants, and for another purpose; while, in the case of the superior animals, including Man, we have only incomplete and disjointed observations, scarcely transcending mere popular notions.

Thermological action.

After the mechanical influences, we reach one which affects structure-the thermological action of the medium. It is the best known of all; for nothing is plainer than that life can exist only within certain limits of the thermometrical scale, and that there are limits affecting every family, and even every living race; and again, that the distribution of organisms over our globe takes place in zones sufficiently marked, as to differences of heat, to furnish thermometrical materials to the physicists, in a general way. But, amidst the multitude of facts in our possession, all the essential points of rational doctrine are still obscure and uncertain. We have not even any satisfactory series of observations about the thermometrical intervals corresponding to the different organic conditions;-much less

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