THE BLOOD. 201 



in combination with cholesterin; glycerin normally exists in the 

 blood, 0.001 parts in a 1000. 



The Coloring Matter. The serum is colored yellow by a body 

 which belongs to the luteine group, and is often called lipochrome 

 or seroluteine. 



Enzymes. There are several ferments, as lipase, anti-ferments; 

 also alexins, haemolysins, precipitins, etc. 



Lactic acid is also found, which is, in part, dependent upon meat 

 in the diet. Its quantity varies from 0.17 per cent, to 0.5 per cent. 



COAGULATION OF THE BLOOD. 



Normal blood contained within the body vessels is a fluid. For 

 a very brief period after it makes its exit from a wounded vessel it 

 remains in a liquid state, but within two or three minutes its 

 viscidity increases until there is formed a solid of the consistency 

 of jelly; to this has been given the name blood-clot. The process 

 whereby the clot is formed is termed coagulation, and is caused by 

 the presence of a body called fibrin. 



To best observe the process of coagulation, the blood is drawn 

 into an open vessel, a beaker. The initial change, which occurs 

 within the first two or three minutes, is the formation of a jelly-like 

 layer over the surface of the blood; during the next three or four 

 minutes this layer extends to such a degree that the entire blood- 

 mass becomes enveloped. If at this time the contents of the vessel 

 be turned out, they form a mold of the exact shape of the contain- 

 ing vessel, or the vessel may be inverted without the escape of the 

 contents. This jelly-like mass is the clot. Within it are imprisoned 

 the serum and corpuscles. 



A straw-colored fluid, the serum, is expressed, appearing upon 

 the surface to form finally a transparent layer of liquid around the 

 clot. The retraction is complete at the end of from twelve to 

 twenty hours, at which time all of the serum has been expressed and 

 the corpuscles enmeshed within the network of fibrin. The clot, so 

 dense that it may readily be cut with a knife, being heavier than 

 the serum, is found at the bottom of the vessel. It is now just 

 about one-half of its original size. The serum, when examined, is 

 found to be practically free from corpuscles. The character of the 

 clot varies according to the state of the blood. It is large, soft, and 

 tears easily at times. At other times it is small, resistant, and from 

 1li<> energetic contraction of the fibrin the edges of the upper sur- 

 face of the clot curve over so as to form a sort of cup. 



