amongst the particles of fibrin ensues, giving rise to the formation of what are now called fibrinous concretions. It has been shewn, also, that when the circulation of blood is completely arrested in its course through the vessels, as when a ligature is applied, the formation of a coagulum of blood at the obstructed point is the ordinary fact; again, that in aneurism, where the current is impeded from its passing through a dilated vessel, a deposition of the fibrin is common at the most depending part, as a result of the languid motion; nay, more, that any direct obstacle to the course of the blood in its vessels, say an indurated valve, or a thread stretching across an artery or vein, is sufficient, under some conditions, to produce at the point where it obstructs a kind of coagulation.

cess.

In the second place, it has been very properly urged, that the mere act of suspending coagulation for a time by the agitation of blood in a closed vessel, is a proof that absolute rest has to do with the coagulating proFor, although the fibrin may either eventually cling to the side of the vessel in which the agitation is kept up, or float to the top of the fluid, these results are slowly induced, and depend, indeed, on the fact, that the fluidity of the blood has been kept up for a length of time sufficient to permit the red corpuscles to subside, and the fibrin to exert at leisure its specific property of molecular attraction.

Thirdly, the experiments which shew that the blood in a glass tube affixed by its two extremities to the free ends of a divided artery, does not coagulate, so long as it is passing through the tube, have been adduced in favour of the correctness of the theory now being considered.

Against it there stand out in bold relief; first, the valid objections derived from the facts Hewson discovered and dwelt upon so forcibly, viz., that blood retained in a state of rest in a vein coagulates very slowly so long as it is thus confined. Secondly, that blood extravasated into the living cellular tissue may remain fluid for weeks, though at perfect rest, but being let out will coagulate while still at rest in the receiving vessel. Thirdly, that blood drawn from the body cannot, by any kind of motion or agitation, be held in the same fluid condition as during life; i. e. with its fibrin distributed throughout the whole fluid as a part of the homogeneous liquor sanguinis. To all these arguments double force is added by the overwhelming evidence in favour of the view, that, in the circulating system, during healthy states, the fibrin is as certainly in solution as is the albumen or the soluble salts. If so, then, the force which can thus hold fibrin soluble is sufficient of itself, is chemical rather than physical in kind, and is independent of motion.

Such is the conflicting evidence on the subject of the stasis theory of coagulation. Fact meets fact in collision. Taking it all in all, however, unless something more can be said in its favour, the theory fails to account in full for the phenomenon of coagulation. But like the theory relating to exposure to air, it may comprise so much of truth, that, in the presence of the whole truth, the arguments and facts on which it has been founded would be easily read off and understood.

Hypothesis of the Vital Principle. If writers who speak of a vital force, or principle, could define what they mean by the term, or could even agree to a kind of

hypothetical definition in regard to it, we might be able to treat more satisfactorily of this hypothesis. Or if, in using the term "vital principle or force", they would rest content to let it stand to express, in a general sense, the aggregate of all the phenomena observed in the living body; or if they would only use the term to explain any operation, whether chemical or physical, which occurs in the body, simply because it does occur in it; if these definitions were admitted, there would be fewer difficulties in the way. But so far is this from being the case, that we find even those who speak of the vital principle in connexion with coagulation, assigning to it two distinct and directly opposite functions. It is plain that Mr. Hunter held the vital principle, i. e. its presence, to be the cause of coagulation; for he compares the change that occurs in the blood removed from the body to certain transformations or changes which occur to it in the body during life. On the opposite principle, the older physiologists thought that the living blood was retained in a state of fluidity by the presence of the vital force, and that the act of coagulation, in blood at rest, arose purely from the loss of the vitality which ensued upon its removal from the living structures; and it is evidently towards this latter view of the vital hypothesis that Mr. Thackrah, Franz Simon, and even Dr. Carpenter, incline. Our modern physiologists are, however, much less consistent than were those of old; for, although they defend the idea of the existence of some peculiar principle, or entity, which they call vital, they at the same time do not omit the attempt to explain the nature of the vital act itself on physical or chemical grounds. Into this peculiar mode of reasoning Dr. Carpenter very obviously falls, without seeming to

be conscious that to offer a physical or chemical explanation of any obscure phenomenon, is to admit that the phenomenon itself is the result of physical or chemical causes. Thus, unhappily, whenever a very hard and peculiar problem relating to organised structures has to be solved, writers are apt, in a dilemma, to beg the question by referring the cause of the phenomenon to the "vital principle" as to an entity, or ruling force, which, being vital, is open to any definition, or to none. It is clear, however, that to bring a problem to such an ultimatum as this, is merely equivalent to saying that nothing is or can be known about it. For, as the physiologist is prevented by the limitations of his science from instituting any but chemical or physical inquiries as to the causes of natural phenomena, it were vain for him to institute such inquiries at all, unless he felt that by them he might unlock possibly a chemical or physical secret bearing on the point. Nay, should he fail by such inquiries to solve the questions before him, what would this negative result indicate? That the cause of a phenomenon is referrible to an indefinable principle? Certainly not. But rather that his knowledge of physical or chemical laws is simply insufficient for carrying him to the goal he has in view.

In relation to coagulation of blood, the vital hypothesis is entirely disproved; nay, it would never have been advanced but for the coincidence that the phenomenon occurs in blood newly drawn, and without man's interference. If an experiment were wanted, if blood had to be raised in temperature to 150° or 160°, to make its fibrin coagulate, in the same way as is necessary with the serum when its albumen is made to coagulate by heat, the idea of vitality would be ridiculous.

Yet the albumen of the serum comes from the living body the same as the fibrin. But why argue the point thus, when experiment answers for itself? Hewson, Hunter, John Davy, and others, have frozen blood, and have kept it, thus frozen, from coagulating. They have then thawed the frozen mass, and the fluid has thereupon coagulated. Does the coagulation of blood that has been frozen (and even frozen and thawed three times successively) depend on the presence of vitality, or on the loss of vitality?

One further disproof is conclusive, without more. Dr. Davy and Mr. Gulliver have both shown that fresh blood may be held fluid for weeks by the addition to it of certain salts, and may then be made to coagulate by the addition of water. "Some horses' blood," says Gulliver," which I had kept fluid with nitre for fiftyseven weeks, readily coagulated when diluted with water." Did this blood, kept fluid fifty-seven weeks, coagulate from the presence or from the abstraction of the vital principle? With this query the hypothesis of the vital force may be safely left to its advocates, for once and for good.

Hypothesis of a Nervous Force. The idea that the nervous system supplies something to the blood which keeps it in the fluid state, though less mystical than the vital hypothesis, is still very poor and improbable. What is the nervous force? Is it analogous to electricity? If so, then the effects of electricity on drawn blood shew nothing positive on the subject. Is it a force in itself special? If so, how does it affect the blood, and where? Instead of the "nervous influence" keeping the blood in a fluid state, from what we know regarding the effects of cutting off the nervous commu