CHEMIC COMPOSITION OF THE HUMAN BODY. 21 



4. COAGULATED PROTEIDS. 



Although these proteids are not found as constituents of the animal 

 organism, they possess much interest on account of their relation to 

 prepared foods and to the digestive process. They are produced when 

 solutions of egg-albumin, serum-albumin, or globulins are subjected 

 to a temperature of 100 C. or to the prolonged action of alcohol. 

 They are insoluble in water, in dilute acids, and in neutral saline 

 solutions. In this same group may be included also those coagulated 

 proteids which are produced by the action of animal ferments on 

 soluble proteids e. g., fibrin, myosin, casein. 



(a) Fibrin. Fibrin is derived from a soluble proteid fibrinogen 

 by the action of a special ferment. It is not present under 

 normal circumstances in the circulating blood, but makes its 

 appearance after the blood is withdrawn from the vessels and 

 at the time of coagulation. It can also be obtained by whipping 

 the blood with a bundle of twigs, on which it accumulates. 

 When freed from blood by washing under water, it is seen to 

 consist of bundles of white elastic fibers or threads. It is in- 

 soluble in water, in alcohol, and ether. In dilute acids it swells, 

 becomes transparent, and finally is converted into acid-albu- 

 min. In dilute alkalies a similar change takes place, but the 

 resulting product is an alkali-albumin. Fibrin possesses the 

 property of decomposing hydrogen dioxid, H 2 O 2 i. e,, liberating 

 oxygen, which accumulates in the form of bubbles on the 

 fibrin. On incineration fibrin yields an ash which contains 

 calcium phosphate and magnesium phosphate. 



(&) Myosin. Myosin develops in muscles after death and is the 

 cause of the stiffening of the muscles. It has been regarded 

 as a derivative of the soluble proteid myosinogen alone, but 

 there is evidence that in its formation both paramyosinogen 

 and myosinogen take part. It is not definitely known whether 

 this is the result of the action of a special ferment or not. 

 (c) Casein. Casein is derived from the chief proteid of milk 

 caseinogen by the action of a special ferment known as 

 rennin or chymosin. This ferment is a constituent of gas- 

 tric juice. 



5. PROTEOSES AND PEPTONES. 



During the progress of the digestive process, as it takes place in 

 the stomach and intestines, there is produced by the action of the 



