THE CHEMICAL COMPOSITION OF MILK 25 



separation, together with products of their decomposition dur- 

 ing the process used for their removal." 

 Fibrin (Babcock). 



Fibrin is a nitrogenous substance found in blood shortly after 

 it is removed from the body, and to it the spontaneous coagula- 

 tion of blood is due. It is not found in the living organism, 

 except under abnormal conditions when the circulation is 

 obstructed. The coagulation of blood is facilitated by warmth, 

 by exposure to air, and by contact with foreign substances, 

 especially if such substances have a rough surface. Under the 

 microscope the clot has a threadlike appearance, the threads 

 crossing each other irregularly, forming a fine network. 



The coagulation of blood is retarded by cold and prevented 

 by rapid freezing ; the coagulation, however, takes place if the 

 blood be again warmed. The coagulation may be prevented 

 by certain chemical reagents, among which may be mentioned 

 the caustic alkalies, magnesium sulfate and potassium nitrate. 

 Freshly coagulated fibrin decomposes the peroxide of hydrogen, 

 oxygen being set free. This power is weakened by prolonged 

 exposure of the fibrin to air and is destroyed when the fibrin 

 is exposed for a short time to heat which approaches the boiling 

 point of w r ater. 



The evidence that fibrin is formed in milk may be summed 

 up as follows : 



(1) The peculiar grouping of the fat globules shortly after 

 the milk is drawn, the grouping being entirely analogous to 

 that of the blood corpuscles in blood. When milk is first drawn 

 the globules are entirely separate, and if the milk be received 

 in a vessel containing a substance that will prevent the coagu- 

 lation of fibrin, no grouping of the globules will occur. 



(2) The decomposition of hydrogen peroxide by milk, the 

 action not taking place with milk that has been heated to near 

 the boiling point. 



(3) The general phenomena of the creaming of milk. Those 



