REST AND MOTION.

Another theory on the process of coagulation has been that it arises simply from absolute rest. I do not know who originated this theory; but it has been referred to incidentally by various authors. Thus Lancisi, in speaking of aneurism, remarks on the separation and coagulation of glutinous chyle in aneurismal cavities; and implies that, as this is merely held in mechanical suspension in the blood, it is prone to separate and become deposited whenever the motion of the blood is slow. He compares an aneurism to a lake formed in the course of a river; and concludes, that as the insoluble substances, which are mechanically suspended in the natural current of the river, where the motion is rapid, are laid down on the sides of the lake, where the motion, from well known dynamical causes, is slow, so the blood, when flowing through the arteries, holds in suspension its solid constituents, while, in flowing through an aneurism, where the motion is impeded, it deposits these constituents on the sides of the sac. Rest and cold were assigned by Davies as the causes of coagulation.

Dr. S. Collins, in his work on Anatomy, written in 1685, contends that polypous concretions in the heart are identical in structure with the buffy coat of coagulated blood, and that they arise from a languid motion of the blood current, being deposited from the blood in a manner analogous to the formation of stone in the bladder. Dr. Brown, too, writing in 1684, remarks that depositions of fibrin and firm clots of blood are most commonly found on the right side of the heart, and most frequently in the right auricle; an effect due mainly to the slow motion of the returning blood through these parts of the circulation. Spallanzani

also taught indirectly that rest is the cause of coagulation; since blood stagnates and coagulates most quickly where its motion is slowest, as in the extreme. parts of the circulation. The same view has been supported by more modern physiologists and pathologists, who have argued that the tendency to coagulate is greatest in weakened animals. Magendie, who entertained a similar opinion, made an experimental trial by introducing a tube into the two extremities of a divided artery, and found that the blood remained fluid only so long as the action of the heart continued to drive. it forward. Magendie also, with J. Simon and Carswell, refer to the experiment of passing a ligature, or needle, transversely through an artery, and to the fact, that a coagulum of fibrin forms upon the foreign substance thus introduced into the circulating current. On a similar basis of reasoning, reference has often been made to the frequent coagulation of blood on the valve cords of the heart, on indurated valves, and on any other points in the circulatory apparatus which, from retarding the blood current, form favourable points d'appui for the formation of fibrinous clots.

Dr. Bostock, in summing up the causes of coagulation, supports the view that the procees depends on cessation of motion. He remarks, "that, as fibrin is gradually added to the blood, particle by particle, while this fluid is in a state of agitation in the vessels, it has no opportunity of concreting; but when it is suffered to be at rest, either within or without the vessels, it is then able to exercise its natural tendency. In this respect,” he adds, "the coagulation of the fibrin of the blood is very analogous to the formation of organised solids in general, which only exercise their property of concreting or coalescing under certain circumstances, and when

those causes, either chemical or mechanical, which would tend to prevent the operation, are not in action. Upon this principle, we shall be induced to regard. the coagulation of the blood as analogous rather to the operation by which the muscular fibre is originally formed, than to that by which its contractile power is afterwards occasionally called into action."

On the other side, it has been forcibly urged that the mere statical condition of the blood has little, if anything, to do with its coagulation. The fact stated by Hewson, and supported by Scudamore, and lately by Stromeyer, that if a portion of blood be tied up in the vein of a living animal it does not coagulate for some hours, unless let out, when it may coagulate rapidly, is thought by some to settle negatively the stasis theory. Instances have been related, moreover, where blood effused into the cellular tissue, or other soft parts, has remained fluid for weeks, and has coagulated immediately on being let to escape into a vessel. There have thus been adduced, to oppose the theory of rest as a cause of coagulaion, the very arguments which have been brought forward by its supporters as fully substantiating their idea. It has been further urged, that if the particles of fibrin were merely mechanically suspended in the blood, they would be as easily distinguishable by the microscope in an isolated form as are the blood corpuscles. Some interesting inquiries on this point, favouring the mechanical suspension view, have been made by Dr. A. Buchanan; and Dr. Milne Edwards is inclined to believe that fibrin, like the proper globules, is merely suspended in the mass of the blood in a state of extreme subdivision, and possessed of transparency too perfect to be distinguished in the surrounding fluid.

VITAL FORCE.

The idea that the coagulation of the blood is due to some peculiar principle of vitality, is included in the well known hypothesis of John Hunter. However carefully the works of this physiologist are studied, one finds a difficulty in understanding what he precisely meant by the "vital principle," or its effects in promoting the coagulation of blood. In one sentence he remarks, "This disposition to coagulate, when out of the vessels, or when retained in them without motion, till the consciousness of the use of motion, and, of course, of fluidity, is lost, is one of the effects of the life of the blood." This sentence, obscure as it is, includes, as fully as any other, Hunter's view. That he himself was not satisfied, is obvious; for he proceeds to remark on the use he has made of the word "consciousness," explaining that he has employed that term because we have no language existing answerable to all his views of the animal economy; and that to coin words. would not answer his purpose, because he must then have a dictionary of his own. In a further sentence, Hunter speaks of coagulation "as a species of generation, or as the first action or establishment of a power of action within itself, so as to form itself into muscular fibres-the only powers in an animal." The only explanation of this hypothesis that can be arrived at, is, that it supposed to exist in the body a separate principle or entity, which, although taking part in, and overruling all the organic processes, is yet distinct from them, and is itself unmodified by the changes it excites. This principle, therefore, acts on the blood in the body so as to form it into the various structures;

but when blood is removed from the vessels, this fluid, being still acted on by the living principle, undergoes coagulation-an analogous phenomenon.

In order to add force to his hypothesis, Hunter relates several cases, where death took place from the instantaneous and complete abstraction of the presumed vivifying principle. A gentleman in perfect health dies instantaneously from passion; and death takes place in every part at once. A healthy woman, in giving birth to a child, dies instantaneously. A soldier receives a blow on the pit of the stomach, and succumbs at once. An animal is struck dead by lightning. Two deer are hunted to death; in which case they acted till every power of action ceased. In all these cases, the blood was in a fluid state, and did not coagulate on being exposed; and the muscles were not rigid-a result due to the rapid abstraction of the life of the solids and of the blood. In other cases, he adds, where an animal dies in the common way, the vital actions are first destroyed, but life still exists: for the muscles contract and the blood coagulates.

In other parts of his works, Hunter dwells on the same hypothesis. "Coagulation," he remarks, "I conceive to be an operation of life; and I imagine it to proceed upon the same principle as the union by the first intention. It is particle uniting with particle by the attraction which in the blood forms a solid."

To these opinions of Hunter, regarding a vital influence, strict obedience was for many years paid. They lost ground as the labours of Magendie became more prominently marked, and as the solution of the chemical problems of life advanced. In these present days, they are again being reverted to. Franz Simon, in his