CHAPTER V. 



THE CLOTTING OF BLOOD. 



The Coagulation of the Blood. "When blood is first 

 drawn from the living Body it is perfectly liquid, flowing 

 in any direction as readily as water. This condition is, 

 however, only temporary ; in a few minutes the blood be- 

 comes viscid and sticky, and the viscidity becomes more 

 and more marked until, after the lapse of five or six min- 

 utes, the whole mass sets into a jelly which adheres to 

 the vessel containing it so that this may be inverted without 

 any blood whatever being spilled. This stage is known 

 as that of gelatinization and is also not permanent. In 

 a few minutes the top of the jelly-like mass will be seen 

 to be hollowed or "cupped" and in the concavity will be 

 seen a small quantity of nearly colorless liquid, the blood 

 serum. The jelly next shrinks so as to pull itself loose 

 from the sides and bottom of the vessel containing it, and 

 as it shrinks squeezes out more and more serum. Ulti- 

 mately we get a solid clot, colored red, and smaller in size 

 than the vessel in which the blood coagulated but retain- 

 ing its form, floating in a quantity of pale yellow serum. 

 if, however, the blood be not allowed to coagulate in per- 

 fect rest, a certain number of red corpuscles will to rubbed 

 out of the clot into the serum and the latter will be more 

 or less reddish. The longer the clot is kept the more serum 

 will be obtained: if the first quantity exuded be decanted 

 off and the clot put aside and protected from evaporation, 

 it will in a short time be found to have shrunk to a smaller 

 size and to have pressed out more serum; and this goes on 

 as long as it is kept, until putrefactive changes commence. 



