SO

influence are identical with those which attend the communication or withdrawal of that physical agent with which we have been already occupied, identical, indeed, that we naturally inquire whether the higher and mystical force does not operate through, and by means of, this ordinary agent. Independently of any unintelligible theories on the subject, it would appear that the peculiar nature of the nervous system, and the relation which this system holds to the rest of the organism, would authorize such a conjecture. The composition is of cells and fibres, constructed upon a common type, and moulded from a common plasm, with the other parts of the body; and structurally, therefore, there is no sufficient reason to suppose speciality of attributes. Nerve and ganglion, also, dissolve away under the ordinary destructive agencies which act upon the body, and change into new chemical compounds, identical in nature and history with the compounds which result from the disintegration of the rest of the organism. Viewing the question, therefore, in connexion with genesis, as in the act of nutrition elsewhere, a certain amount of ordinary physical force must attend the formation of nervous matter: and viewing it in connexion with destruction or disintegration, or, in other words, in relation to the respiratory function, the chemical affinity, which is here in active play, is but another name for the same force. A proportionate destruction of tissue is

also involved in the development of nervous influence; and in this respect, as in other varieties of force, the nervous influence may be regarded as the exponent of a certain condition of change in matter.

For these reasons it must be admitted that ordinary physical agencies constitute a part, at least, of nervous power; nay, more, that the degree

of the one is commensurate with that of the others. It is impossible, moreover, to conceive the idea of ordinary force being present and inoperative; and it can scarcely be imagined that the nervous power which is superadded to the more commonplace agents should have a different law of action, otherwise the one might negative the other. Whatever difference of essence, reason and experience argue a community of operation; for, so far as the capillary vessels are concerned, the effects of an insufficient or excessive supply of nervous influence are similar to those which attend equivalent alterations in the intensity of ordinary force. Such, indeed, are the facts already cited in connexion with the history of fear and joy as to allow it to be supposed that the nerves act upon the capillaries-not by the sur-addition of any new agency, but by means of that which is already in operation, by that, namely, which is the necessary exponent of the molecular changes in the material part of the nervous substance.

The metaphysical arguments which concern the

relation between physical and vital force have been set forth elsewhere, and to these we must refer the student for the other arguments which bear upon this subject. At present, however, we have only to do with physiological facts and considerations; and these, we may observe, are of such a character as to allow us to suppose an intimate relation between the nervous influence, physically considered, and the ordinary force of matter, so intimate, indeed, that the former may be regarded as a mere modification of the latter, not essential to the functions of vegetables, or of the lowest tribes of animate existence, but superadded in order to intensify the vitality of higher and more favoured creatures. It remains to be seen whether a subsequent examination of the phenomena of vital motions will bear out this conjecture, and the judgment must be suspended until the special modes of the operation of force upon the heart and the muscular system generally have been passed in review.

(b.) Of the organic force, not of a nervous character, as an agent in the capillary movements of animal bodies.

The force here referred to is of a twofold nature: on the one hand, it is the exponent of the changes which constitute the function of nutrition; and on the other, it marks the molecular movements of respiration.

The operation of the force originating in nutrition may be seen in the phenomena of capillary circulation, if we contrast the opposite conditions of inflammation and anæmia. The abstract idea of inflammation consists, as it were, in the emancipation of some of the smaller vessels from their subservience to the heart-in the return to an early type of circulation -and in the establishment of an unnatural focus of movement, to which an undue afflux of blood is determined. In this state the vessels exhibit the highest degree of vitality, and are fully distended with blood; while, at the same time, the increased manifestation of heat shows that this condition is attended with an inordinate amount of common force. In anæmia, on the contrary, where the watery blood is insufficient to the fit discharge of the function of nutrition, the capillaries are shrunk and exsanguine; and this condition is always accompanied with an absence of the natural degree of animal heat. Contrasting, therefore, the history of inflammation with the opposite state of anæmia, we may, without the assumption of any unintelligible agency, explain the peculiar condition of the vessels at the time, as the natural consequence of the degree of ordinary force resulting in the nutrient changes, to which at the time the vessels are subjected.

The history of the function of respiration is written in such plain terms, that it can scarcely be doubted

that the accompanying force, which is its exponent, is ordinary and mechanical in its characters. The essence of this function consists in the formation of water and carbonic acid by the union of the oxygen of the atmosphere with certain hydrogen and carbon constituents of the organism; and, as the volume of the products is less than that of the constituent elements, it follows that the extrication of a certain amount of heat must attend their formation; and hence there can be no doubt that the force operating upon the vessels may be ordinary force. And that such is its nature may be ascertained, if the subject be fully analyzed.

What, it may be asked, is the true and essential character of the function of respiration? On a first glance at the physical and chemical nature of the act, without any reference to ulterior consequences, it would not seem to differ widely from the ordinary processes of combustion and decay. The atmosphere acts in the same way in each case, and the products which mark the action are similar; and except a mere question of degree, the only difference would appear to be, that in the one case the dissolution of the bodily fabrics is slow and gradual, and masked by the deposition of new matter in the function of nutrition, while in the other the disorganization is more rapid, and altogether undisguised by the counteracting function.

The parallelism of the acts of decay and respiration