COAGULATION OF THE BLOOD. 143 



posed, as we have seen, of clear plasma, holding corpuscles in 

 suspension ; but these little bodies do not differ much from 

 the plasma, either in consistence or specific gravity, and give 

 to the fluid only a slight degree of viscidity. Shortly after 

 the circulation is interrupted, or after blood is drawn from 

 the vessels, it coagulates or " sets" into a jelly-like mass. In 

 a few hours we find that contraction has taken place, and a 

 clear, straw-colored fluid has been expressed, the blood thus 

 separating into a solid portion, the crassamentum or clot, and 

 a liquid, which is called serum. The serum contains all the 

 elements of the blood except the red corpuscles and fibrin, 

 which together form the clot. Coagulation takes place in 

 the blood of all animals, commencing a variable time after 

 its removal from the vessels. In the human subject, accord- 

 ing to JN^asse, 1 when the blood is received into a moderately 

 deep, smooth vessel, the phenomena of coagulation present 

 themselves in the following order : 



First, a gelatinous pellicle forms on the surface, which 

 occurs in from 1 minute and 45 seconds to 6 minutes ; 

 in from 2 to 7 minutes a gelatinous layer lias formed 

 on the sides of the vessel ; the whole mass becomes of 

 a jelly-like consistence in from 7 to 16 minutes. Contrac- 

 tion then begins, and if we watch the surface of the clot we 

 will see little drops of clear serum making their appearance. 

 This fluid increases in quantity, and in from 10 to 12 hours 

 separation is complete. The clot, which is heavier, sinks to 

 the bottom of the vessel, unless it contain bubbles of gas, or 

 the surface be very concave. In most of the warm-blooded 

 animals the blood coagulates more rapidly than in man. It 

 is particularly rapid in the class of birds, in some of which 

 it takes place almost instantaneously. Observations have 

 shown that coagulation is more rapid in arterial than in 

 venous blood. In the former the proportion of fibrin is 

 notably greater. 



1 MILNE-EDWARDS, Lefons sur la Physiologic, etc., tome i., p. 125. 



