162 THE BLOOD. 



son, why the blood coagulates in the body after death. Under 

 the circumstances in which it is then placed, the escape of 

 volatile substances, though retarded, is evidently not pre- 

 vented. Thus when the body is opened shortly after death, 

 we may find the blood perfectly fluid, coagulating, however, 

 shortly after it is removed from the vessels and exposed to 

 the air. During life, when circulation is arrested or much 

 retarded, the blood will coagulate ; but here there is the same 

 opportunity presented for the escape of volatile matter. As 

 ammonia is undoubtedly received by the blood in the course 

 of circulation, arrest of circulation in any part of the vascular 

 system prevents the blood therein contained from receiving 

 its constant supply. As it has been shown that out of the 

 body the evolution of ammonia always accompanies coagu- 

 lation, we must infer simply that coagulation in the body, 

 under the above-mentioned circumstances, is attended with 

 the evolution of this principle, for the conditions here do not 

 admit of direct experimentation, situated as the blood is in 

 the midst of tissues, from which volatile substances are also 

 evolved. It is not proper, however, to shut our eyes to the 

 fact that blood eft used into the tissues and into the cavities, 

 during life, has been known to remain fluid for days and 

 even weeks, when there are no circumstances which we can 

 appreciate as modifying or preventing the gradual evolution 

 of ammonia. But we know that there are many animal 

 products, such as the vaginal mucus, etc., which prevent 

 coagulation ; and in these instances, which are not very fre- 

 quent, it has not been shown that some influence of this kind 

 was not brought to bear on the process. It is a curious fact, 

 also, that leech-drawn blood remains fluid in the body of the 

 animal. Eichardson has verified this fact, but says that he 

 can offer no satisfactory explanation. He observed also that 

 the blood flowing from the leech-bite presented the same 

 persistent fluidity, which explains the well-known fact that 

 the insignificant wound gives rise to considerable hemorrhage. 

 On this point he has made the following curious experiment : 



