734 BLOOD lates in two or three minutes after having been drawn from a blood vessel. 7. Dr. B. W. Kichardson of London some years ago obtained the great Astley Cooper prize for a paper on the cause of the coagulation of the blood, which he attributes to the separation from the blood of a principle which he thinks always exists in circulating blood. This principle is the car- bonate of ammonia. The proofs of this theory are that the author has always found this sub- stance given out by the blood at the time it coagulates, and that when this substance is kept by the blood it remains liquid. Zimmer- mann has published a paper to show : 1, that the discovery of the constant presence of am- monia in the blood belongs to himself; 2, that there are many facts which are in opposition to the view of Dr. Richardson. These views seem not only improbable, but in opposition' to many facts. 8. We come now to the most probable cause of the coagulation of the blood, and the only one which in the present state of science has no fact against it, and seems, on the contrary, to agree with all the facts. This cause is a negative one; it is the absence of a peculiar influence on the blood that, according to the theory, produces, or rather allows co- agulation. It is supposed that fibrine natu- rally tends to coagulate, and that some pecu- liar influence of the living tissues prevents its doing so. Sir Astley Cooper, Thackrah, and others, have been led to consider this view as probable. They found that blood kept an hour in a vein, between two ligatures, was still fluid, while it coagulated in from two to four minutes when extracted from the vessel. Gul- liver has seen also that blood is very slow to coagulate when confined in a vein of a living dog. Brown-Sequard has found blood still liquid, after many months, in the veins of dogs, where it had been confined after the ap- plication of two ligatures, and he has ascer- tained that this blood coagulated in a few minutes after having been abstracted from the veins. It is well known that blood effused everywhere in the bodj' frequently remains liquid, and also that in leeches it sometimes does not coagulate, while in all these cases as soon as the liquid blood is separated from the living tissues it becomes solid. Coagulation is slow even in the blood vessels and heart of a dead animal or man. But all these facts lead only to the conclusion that a peculiar influence of tissues and organs during life, or a little after death, has the power of preventing co- agulation ; they do not show what is this pe- culiar influence. Thackrah thought it was the vital or nervous power of the tissues. Briicke has shown that even when the heart has lost its vital properties, it keeps the blood fluid, and he has arrived at a theory which we do not think yet fully proved. He maintains that there is no such thing as liquid fibrine in liquid normal blood, and that coagulated fibrine is the result of an atomic change in some part of the albumen of the liquor sanguinis. We will cc include our examination of the facts and theories concerning the cause of the coagula- tion of the blood, by saying that there is in the blood vessels, and in the heart, and also in other tissues, some physical or chemical influ- ence which maintains the blood fluid, and that when this influence is removed the blood co- agulates. Schroeder van der Kolk had ima- gined that coagulation of the blood was pre- vented by an influence of the cerebro-spinal nervous centres on the blood through the blood vessels, and he thought he had proved the correctness of this view in finding that when he destroyed the brain and the spinal marrow, | coagulation quickly took place in the blood.
- But Brown-Sequard has found that the de-
struction of the spinal marrow in the whole length of its lumbar enlargement, in birds and cats, not only did not produce coagulation ] of the blood, but did not immediately kill the animals, many of which have lived many months after the operation. When the ar- teries or veins are changed in their structure by an inflammation or other disease, they lose their power of preventing coagulation. 9. Coagulation is hastened or immediately de- termined by certain substances. J. Simon has seen it take place on threads kept in the current of blood in veins and arteries in living animals. Dupny and De Blainville have seen coagulation quickly produced in blood after the injection of cerebral matter. II. Lee has seen the same thing after injection of pus, and Virchow and others after injection of mer- cury and other substances. Iodine and iodides and galvanic currents hasten coagulation, and have been employed, on account of their influ- ence on blood, for the cure of aneurisms. 10. Coagulation is retarded or entirely prevented by certain substances. Neutral salts act in this way, as well as many medicines and poi- sons, such as opium, belladonna, aconite, hy- oscyamus, digitalis, strong infusions of tea and coffee, &c. Gulliver has kept horses' blood I liquid for 57 weeks by the influence of nitre, and this blood rapidly coagulated when it was diluted with water. This fact explains how in some cases blood does not coagulate in the body after death. So it is particularly after drowning, or death by irrespirable gases, or poisoning by cyanhydric acid, &c. But if the I following fact, mentioned by Polli, be true, it is possible that, in some of those cases where blood has been found fluid in the veins long after death, the coagulation would have been observed taking place at a later period if the blood had been kept long enough. Polli says he has seen blood remain liquid a fortnight and then coagulate spontaneously, and he thinks that blood will always be found to co- agulate if kept long enough. 11. The surface of a clot of blood very often presents a more or less considerable layer of coagulated fibrine nearly free from red corpuscles, and conse- quently without color; this layer is what is called the buflfy coat. We owe to Gulliver the
