CHAPTEE 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 becomes viscid 

 and sticky, and the viscidity becomes more and more marked 

 until, after the lapse of five or six minutes, 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 though retain- 

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

 however, the blood be not allowed to coagulate in perfect rest, 

 a certain number of red corpuscles will be 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 until putrefactive changes 

 commence. 



Cause of Coagulation. If a drop of fresh-drawn blood 

 be spread out- very thin and watched for a few minutes with a 

 microscope magnifying 600 or 700 diameters, it will be seen 

 that the coagulation is due to the separation of very fine solid 

 threads which run in every direction through the plasma and 

 form a close network entangling all the corpuscles. These 



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