\COAGULATION OF BLOOD. 97 



and that as soon as the pressure is discontinued the corpuscle 

 springs back to its former shape, showing that it is elastic. 



The Coagulation of Blood. When the blood escapes 

 from its natural channels it usually changes from a liquid to 

 a jelly-like condition. This is known as Coagulation. It is 

 due to the formation of the threads of Fibrin from the plasma. 

 These threads of fibrin entangle and inclose the corpuscles, 

 and the two constitute the Clot, or Coagulum as it is more 

 technically termed. The liquid that afterward separates from 

 the clot is the Serum, and differs from the plasma only in the 

 removal of the fibrin, which is exceedingly small in quantity, 

 though of great importance in its action. Many experiments 

 have been made, and much has been written about the coagu- 

 lation of the blood, and perhaps its real cause is not yet clear. 

 But we know that the coagulation often serves to stop the 

 flow of blood from wounds, and this is its main use. 



If freshly drawn blood be stirred rapidly with a bundle of 

 wires (perhaps the most convenient stirrer is made by making 

 a little roll of wire screen), there will soon collect on the wires 

 a stringy substance. Thorough washing will soon leave this 

 colorless. It is Fibrin. If the stirring has been done thor- 

 oughly the blood will no longer clot, no matter how long it 

 may stand. .' '' 



The following scheme shows the difference between the 

 liquid blood and the coagulated blood: 



f Plasma . . . j Serum 



Liquid Blood 4 (Fibrin [ Ck)fc . \ Coagulated Blood. 

 ^Corpuscles I J 



Amount and Distribution of the Blood. The blood 

 constitutes about one-thirteenth of the weight of the body. 

 It is alkaline in reaction, and is a little heavier than water. 



