THE BLOOD. 23 



eleven grains. I can advance nothing farther in this part of 

 my subject with precision. Nor can I pretend exactly to de- 

 termine the time at which all the blood between the ligatures 

 is coagulated^ I have indeed opened such a vein at the end 

 of three days, when I foun A a thin white coagulum, which was 

 a mere film ; the serum and red particles having disappeared. 

 But the whole is undoubtedly congealed long before this period. 

 The manner in which the blood coagulates, when at rest in 

 the body, has appeared to me curious, and therefore I have 

 taken the more pains to discover how it happens, especially as 

 it may assist us in judging whether or no it coagulates in the 

 heart, so as to form those substances called polypi (xin). The 



(xin.) Blood generally coagulates much more slowly in contact with 

 the living parts than when removed from them, an effect which Mr. 

 Thackrah a ascribes, I believe hypothetically, to the influence of the 

 nerves in keeping the blood fluid. Mr. Hunter 5 noticed that the con- 

 tact of blood with living vessels retards its coagulation. In the ex- 

 periments of Sir Astley Cooper and Mr. Thackrah c blood kept at rest 

 in a living vein did not coagulate in an hour, while blood similarly con- 

 fined in a dead vein, excluding air, was firmly concreted in a quarter of 

 that time ; and blood from the same dogs, cats, and rabbits, used in 

 Mr. Thackrah's experiments, began to coagulate in from two to four 

 minutes when abstracted and set apart in the usual manner. 



I made some experiments at Chatham, in August, 1837, on the coagu- 

 lation of blood confined in the jugular veins of living dogs, disturbing 

 the parts no more than was necessary to apply the ligatures. Twice 

 only, out of many trials, were small clots observed as early as two hours 

 after the operation. Coagulation generally did not commence before 

 the expiration of three hours ; half an hour later there was com- 

 monly a central clot about one fourth the size of the imprisoned 

 blood ; and the remaining three fourths coagulated in two, six, and 

 seven minutes, in three different instances, when received into a watch- 

 glass. In one trial, the confined blood was wholly fluid at the end 

 of five hours ; in another, after seven hours, the clot was no larger 

 than that just mentioned, and the fluid part of the blood coagulated on 

 exposure in five minutes. In nine hours the blood was completely co- 

 agulated in the right vein of one dog, and only partially so in the left 

 vein of another ; and the fluid portion concreted when exposed in less 

 than eleven minutes. After eighteen hours, in two trials the blood was 

 about half coagulated, and in a third, completely so. At the end of 

 twenty -four hours, coagulation was complete in four trials, and incom- 

 plete in one. 



The pale masses of fibrin called polypi are formed in the heart after 



* On the Blood, ed. 1834, pp. 80, 91. c On the Blood, ed. 1834, p. 85; and 

 b Works, ed. by Palmer, iii, 29. Prater, p. 21. 



