having been cleared by the pursuit of the anterior sciences. Many delays were occasioned in their case by transitory phases which were not understood in the earlier days of positivity, and which need never again arrest experienced investigation. It may be hoped that physiologists will spare their science the useless and humbling delay in the region of metaphysical hypothesis which long embarrassed the progress of physics.

Philosophical character of Physiology.

The true philosophical character of physiology consists, as we have seen, in establishing an exact and constant harmony between the statical and the dynamical points of view,—between the ideas of organization and of life,-between the notion of the agent and that of the act; and hence arises the obligation to reduce all abstract conceptions of physiological properties to the consideration of elementary and general phenomena, each of which conveys the idea of a determinate seat. In other words, the reduction of functions to corresponding properties must be regarded as the simple consequence of decompounding the general life into the different functions,-discarding all notions about causes, and inquiring only into laws. Bichat's conception of the properties of tissue contains the first germ of this renovated view; but it only indicates the nature of the philosophical operation, and contains no solution of the problem. Not only is there a secondary confusion between the properties of tissue and simple physical properties, but the principle of the conception is vitiated by the irrational distinction between the properties of tissue and vital properties; for no property can be admitted in physiology without its being at once vital and belonging to tissue. In endeavouring to harmonize the different degrees of physiological and of anatomical analysis, we may lay down the philosophical principle that the idea of property which indicates the last term of the one must correspond with tissue, which is the extreme term of the other; whilst the idea of function, on the other hand, corresponds to that of organ: so that the successive ideas of function and of property present a gradation of thoughts similar to that which exists between the ideas of organ and of tissue, except that the one relates to the act and the other to the agent. This relation

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Division of the study.

appears to me to constitute an incontestable and important rule in biological philosophy; and on it we may establish the first great division among physiological properties. We have seen how in anatomy there is a division between the fundamental, generating tissue, the cellular, and the secondary tissues which result from the combination of certain substances with this original web; and in the same way must physiological properties be divided into two groups, the one comprising the general properties which belong to all the tissues, and which constitute the proper life of the cellular tissue; and the other, the special properties which characterize its most marked modifications,—that is, the muscular and nervous tissues. This division, indicated by anatomy, strikingly agrees with the great physiological distinction between the organic or vegetative and the animal life; as the first order of properties must afford the basis of that general life, common to all organized beings, to which vegetable existence is reduced; while the second relates exclusively to the special life of animated beings. Such a correspondence at once makes the principle more unquestionable, and facilitates the application of the rule.

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If we look at what has been done, towards the construction of this fundamental theory, we shall find that it is fairly accomplished with regard to the secondary, or animal tissues,--all the general phenomena of animal life being unanimously connected with irritability and sensibility,these being considered as attributes each of a definite tissue and thus, the most marked case is the best understood. But the other division, the properties which are wholly general, belonging to the universal life, are far more important, as underlying the others; and an extreme confusion and divergence exist with regard to them. No clear and satisfactory conception of the second class can be formed while the first is left in obscurity; and thus, the science remains in a purely provisional state, its development having taken place in an order inverse to that which its nature requires.

The functions which belong to the vegetative life are two, the antagonism of which corresponds to the definition of life itself:

Two functions of the organic life.

first, the interior absorption of nutritive materials from the surrounding medium; whence results, after their assimilation, final nutrition; and secondly, the exhalation of molecules, which then become foreign bodies, to be parted with, or disassimilated, as nutrition proceeds. It appears to be an error to make digestion and circulation characteristics of animality; as we certainly find them here in the fundamental sense of both. Digestion is properly a preparation of aliment for assimilation; and this takes place in a simple and almost unvaried manner in vegetable organisms: and circulation, though nothing like what it is in animals, where there is a central organ to effect it, is not less essential in vegetative life, the lowest organism showing the continual motion of a fluid holding in suspension or dissolved, matters absorbed or thrown out; and this perpetual oscillation, which does not require a system of vessels to itself, but may take place through the cellular tissue, is equally indispensable to animal and vegetable existence. These, then, are the two great vegetative processes, performed by properties which are provisionally supposed (after the analysis of M. de Blainville, which is open to some objection) to be three,-hygrometricity, capillarity, and retractility. This analysis shows clearly that the actions which constitute vegetable life are simply physicochemical phenomena; physical as to the motion of the molecules inwards and outwards; and chemical in what relates to the successive modifications of these different substances. Under the first aspect, they depend on the properties, hygrometrical, capillary, and retractile, of the cellular tissue: under the second, and much more obscure at present, they relate to the molecular action which its composition admits. This is the spirit in which the analysis of organic phenomena should be instituted; whereas that of animal phenomena should be regarded. from a wholly different point of view, as we shall see hereafter.

The study of this vegetative life is not even yet rationally organized. We have seen that, in the anatomical view, the vegetable kingdom is regarded as the last term of an unique series,-the various degrees of which differ, for the most part, more widely from each other than any one

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of them from this extreme term. The same conception should direct physiological speculations on the organic life, analyzed uniformly for all living beings: but this has not hitherto been even attempted. Till it is accomplished, no essential point of physiological doctrine can be established, however able may be the investigations carried on, and however valuable the materials supplied. It may be alleged that the phenomena relating to general life may be studied. in the broadest simplicity in vegetable organisms: but it is no more possible in physiology than in anatomy to interpret the extreme cases in the scale by each other without having passed through the intermediate degrees: and the dynamical case is the more difficult of the two: so that the isolated study of the organic life in vegetables cannot illustrate that of the higher order of animals. And one natural consequence of this irrational isolation of the vegetable case is that chemists and physicists have engrossed researches which properly belong to biologists alone. The comparative method, which we have seen to be the characteristic resource of biological philosophy, has not as yet been duly introduced into the general study of organic life, though it is at once more indispensable, and more completely applicable than in the case of animal life. If it were consistent with the character of this Work, we could point out gaps at almost every step, and about the simplest phenomena, which must shock any inquiring mind:-the darkness, doubts, and differences about digestion; and again about gaseous digestion, or respiration;-in regard to which the most contradictory opinions are held :-divergences about the simplest preliminary phenomena of vegetative life, which show how much has to be done before we can undertake any direct investigation into the phenomena. of assimilation and the converse process.

We shall find ourselves even further from

satisfaction if we turn from the consideration Results of organic action. of the functions of organic life to those more compound phenomena which are usually confounded with them, but which M. de Blainville has taught us to distinguish as results from the action of, not one organ or set of organs, as in the case of function, but of the simultaneous action of all the principal organs. Of these results, the

State of composition and decomposition.

most immediate and necessary is the continuous state of composition and decomposition which characterizes the vegetative life. Ignorant as we are of assimilation and secretion, the very questions cannot have been as yet suitably laid down. No one has thought, for instance, of instituting an exact chemical comparison between the total composition of each organism and the corresponding system of alimentation: nor, conversely, between the exhaled products and the whole of the agents which had supplied or modified them; so that we can give no precise scientific account of the general phenomenon of the composition and decomposition of every organism as a necessary consequence of the concurrence of the different functions. We have at present only incomplete and disjointed materials, which have never been referred to any general fact.

Vital heat.

It is acknowledged now that all organisms have, more or less, the character which used to be ascribed to only the highest, of sustaining a determinate temperature, notwithstanding variations of heat in their environment; and this is a second result of the whole of the vegetative functions, which almost always co-exists with the first. But this important study is not only in a backward state, but ill-conceived. Besides the error before noticed, of confounding vital heat with the temperature of the medium, the fundamental character of the phenomenon appears to me to have been misconceived. Its modification by the animal functions can never be understood till it has been studied in its primitive universal manifestation in all living bodies, each of which represents a chemical centre, able to maintain its temperature against external influences, within certain limits, as a necessary consequence of the phenomena of composition and decomposition. This is doubtless the point of view from which the positive study of vital heat must be regarded; and to consider it under the modifications of animal life, is to place the accessory before the principal, and to propose views which are merely provisional, if not erroneous. In the most recent works upon this leading subject, the organic foundations are, it is true, more carefully considered: but the investigation cannot be said to be duly instituted as