Page:The American Cyclopædia (1879) Volume II.djvu/753

 BLOOD 733 from the blood vessels of a living man or ani- mal, was a peculiar action of air. Hewson be- lieved that air had a considerable coagulating influence. In proof of this he relates the fol- lowini; experiments: Having laid bare the ju- gular vein in a living rabbit, he tied it up in three places, and then opened it between two of the i ligatures and emptied that part of its blood. He ' next blew warm air into the empty vein and put another ligature upon it, and, letting it rest , till he thought the air had acquired the same degree of heat as the blood, he then removed the intermediate ligature, and mixed the air with the blood. The air immediately made the ; blood florid where it was in contact with it, as i could be seen through the coats of the vein. In a quarter of an hour he opened the vein and found the blood entirely coagulated ; and "as the blood," says Hewson, "could not in this time have been completely congealed by rest alone, the air was probably the cause of its co- agulation." Brucke says that air blown in the manner mentioned by Hewson usually hastens coagulation, but that it is not always so. Brown-Sequard has ascertained that blood mixed with air blown into the jugular veins of dogs does not always coagulate. In some cases, four months after the operation, the blood was found liquid in the vein between two ligatures. It has been remarked that when blood is placed j in a cup, coagulation begins sooner in the part ; in contact with air than in the interior of the i liquid, but Briicke states that he has seen co- ] agulation begin as quickly in the surface in contact with the walls of the cup. If coagula- tion depended upon a peculiar influence of at- mospheric air, it should not take place when blood is not exposed to air. John Davy and H. Nasse have seen coagulation occur as quick- ly in unexposed as in exposed blood. Scuda- more says even that coagulation is more rapid in a pneumatic receiver, where blood is not submitted to the action of air. From many experiments Brucke has drawn the following conclusions: 1. Air usually hastens the coagu- lation of the blood. 2. Air, when introduced into the heart and vessels of living turtles, does not induce coagulation. 3. The blood of frogs, when deteriorated by the action of the heart or of the other tissues of the animal, and so de- i prived of its free oxygen, sometimes requires atmospheric air for its coagulation. 4. Normal blood needs not the presence of air for its co- agulation. Therefore, and chiefly from the last conclusion, it follows that air is not the general cause of coagulation of the blood. 3. Influ- ence of carbonic acid. Scudamore admits that blood coagulates out of the body chiefly be- cause it loses its carbonic acid, which in this theory is the substance that in the blood main- tains fibrine in a liquid state. Sir Humphry Davy and his brother John made decisive ex- periments against this view. They found that blood exposed only to carbonic acid coagu- lates, though more slowly than when exposed to oxygen. Experiments of Brucke show also that the loss of carbonic acid by the blood is not necessary for its coagulation. 4. Influence of motion and rest. It has been said that blood coagulates out of the body because it is not in motion. If blood received in a bottle is agi- tated as soon as it flows from the vein, it usually seems to remain liquid; but if carefully examined, a great many particles of coagulated fibrine are found in it. When fibrine coagulates in this case, it cannot form long fibres, disposed in a kind of complicated network in the whole mass of the blood ; in consequence of the agi- tation, it forms only small solid particles. The blood effused in the body, or kept in a blood vessel, between two ligatures, in a living ani- mal, frequently does not coagulate, although it is not in motion. It seems, therefore, that rest is not the cause of coagulation of blood, either in the body after death or out of the living body. 5. John Hunter proposed an absurd theory of the coagulation of the blood; but as he grounds his view on interesting facts, al- though most of them are only partially true, we shall examine his theory. He observes: " My opinion is that it (the blood) coagulates from an impression ; that is, its fluidity under such circumstances being improper, or no longer necessary, it coagulates to answer now the necessary purpose of solidity." Trying to prove this untenable theory, he says that when the vital principle of the blood is lost, it does not coagulate, which fact, he thinks, shows that coagulation is a vital action. Animals killed by lightning or by electricity, or those which are run very hard and killed in a state of exhaustion, or are run to death, have not their blood coagulated, according to Hunter. He also asserts that blows on the stomach kill- ing immediately, and deaths from sudden gusts of passion, act in the same way, and by the same cause, i. ., the loss of the vital principle. As regards death by electricity, Scudamore and Brown-Sequard have ascertained that blood coagulates after it, hut the clot is not so hard as in other cases. Gulliver collected many facts to prove that blood may coagulate in all the circumstances mentioned by Hunter; but in most of these cases coagulation was very imperfect. It is extremely probable that blood is then altered in its composition, and chiefly in consequence of alterations in the nervous centres and in the muscles. 6. A view proposed by Zimmermann is quite in opposition to that of Hunter. According to the German chemist, blood coagulates because it putrefies when it is not submitted to the chem- ical influence of living tissues. This view is grounded chiefly on the fact that blood kept liquid by certain salts or other substances be- comes at once or very quickly coagulated when a small quantity of putrefied matter is placed in it. This is certainly an interesting experi- ment, but it does not prove that coagulation depends upon putrefaction, and it seems strange that such a theory should be proposed by a man who knows that sometimes blood coagu-