I. OF MOVEMENTS IN THE CAPILLARY VESSELS.

1. Of extra-organic force as the agent in these

movements.

The changes in the life of hybernating animals are the grand test of the operation of these forces upon the vascular system, for this strange faculty is to be referred simply to the conditions in which the life is passed, and not to any peculiarity in the nature of this life. A common squirrel, for example, which hybernates in high northern latitudes no longer does so if it be removed to a warm climate; but he returns to his old habit if again restored to his former home: and this is the common experience of all creatures which exhibit these phenomena. Nor is there any peculiarity in the organization of these animals, except perhaps a greater delicacy of constitution;-for of several animals to all appearance precisely similar, some are found subject to periodical torpidity, and others not, -and so we may argue that their strange susceptibility to the influence of forces foreign to the organism is merely an exaggerated expression of a sensibility which pervades animate nature.

The manner in which the vessels are affected by these forces may be illustrated by other facts. If, for example, the hand be held to the fire it becomes flushed with blood, and this condition may increase

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until a high degree of inflammatory action is kindled in the part; but if, on the contrary, it be plunged into iced water, the circulation is suspended, and the vessels shrink so completely that the bloodless tissues resemble blanched wax. An effect, in some respects similar, may also be noticed in the skin of persons in whom the circulatory powers are feeble, and the appearance sallow and bloodless during the winter, but who lose their sallowness and become roseate and blooming on the occurrence of summer. In other words it may be said that, in each of these cases, the coats of the vessels expand or contract as heat is imparted or withdrawn.

So far as we are able to judge, this alteration in capacity would seem to extend to all vessels generally, and to be prolonged in duration, and not to be transient and limited to certain points as in the laticiferous system of the plant. The exercise of force in this case, as it would appear, is designed to preserve the vessels as open channels, so as to remove as much as possible any resistance which might impede the action of the heart. In the lower grades of existence, however, the case is different, and also in the earlier periods of the fœtal history of the higher animals, while the heart is as yet a feeble instrument in the propulsion of the nutrient plasm, for under these circumstances the vessels do actually possess a proper power of movement analogous to the focal

powers of the latex vessels: -and in the higher animal when the circulation flags and the heart beats faintly and irregularly, it is interesting to observe that the blood no longer moves in a continuous stream in one direction in the capillaries, but oscillates irregularly to and from certain points, in such a manner as to show a tendency to the revival of those numerous centres of action, which had been absorbed and superseded by the heart.

2. Of intra-organic force as the agent in the capillary movements.

In vegetables the vascular movements are mainly dependent upon the agency of extrinsic force, but in animals the case is altered, and the internal or organic powers gain the ascendancy, except in the hybernating class, where perhaps the influence of the two is nearly balanced.

The internal or organic force may be divided into two principal forms, and each of these will demand separate consideration. The first is connected with the mysterious operations of the nervous system; and the other, which is less vague and indefinite in its character, in the expression of the several molecular changes which constitute the functions of nutrition, respiration, and secretion.

(a.) Of the nervous influence as an agent in the capillary movements.

It is not our purpose to consider the abstract properties of the nervous system, and the high and mystical communion between it and the intelligence of man, but simply to examine the physical relation which exists between this system as matter and the rest of the organism.

The physical mode in which the nervous influence affects the capillary vessels-for there is such a tangible mode of action-may be ascertained without any difficulty. When, for instance, the mind is paralysed by fear, the skin becomes pale and blanched, in consequence of the shrinking of its vessels; and not only so, but if the bodily frame be fragile and delicate, the deadening influence extends to the heart, and a state of syncope or entire suspension of circulation is the result: when, on the other hand, the frame thrills under the excitement of joy, and the nervous power is exuberant, the countenance becomes radiant, the skin is suffused with blood, and the heart beats with increased vigour. These phenomena afford a twofold illustration of the importance of the nervous principle as an agent of life," and of the nature of the agency physically considered.

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As evidenced in the capillary vessels, therefore, the effects of an exuberant or deficient supply of nervous

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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