96 PHYSIOLOGICAL CHEMISTRY 



Fibrinogen has the property of clotting or coagulating, and is 

 responsible for the clotting of the blood. If freshly drawn blood 

 is stirred or beaten, the fibrinogen collects in stringy masses 

 called fibrin. If washed free from corpuscles fibrin is a white, 

 tough, elastic material which gives the usual protein tests. 

 Myosinogen and myosin are the chief proteins of muscle tissue. 



Glutelins. The glutelins are proteins found only in the the 

 seeds of plants. The important members of the group are glu- 

 tenin from wheat, oryzenine from rice, and avenine from oats. 

 There probably are others. They are characterized by being in- 

 soluble in pure water, salt solutions or alcohol. They dissolve 

 in dilute acid or alkali. 



Prolamines. The prolamines are proteins found only in the 

 grains. They have been obtained from all grains except rice. 

 The best known members are gliadin from wheat, zein from corn, 

 and hordein from barley. The group was named because of 

 their high content of proline. The prolamines are characterized 

 by being soluble in 70-80% alcohol. They are insoluble in water. 

 They contain only small amounts of arginine and histidine and no 

 lysine. 



Albuminoids. Albuminoids are proteins obtained from a 

 wide variety of sources in the animal world. Important mem- 

 bers of the group are keratin from horn, nails, hair, hoofs, etc., 

 collagen from connective tissue and bone, its derivative gelatine, 

 which properly does not belong in this class however, and elastin, 

 from ligaments and connective tissue. There also are various 

 other albuminoids. The members of the group are classed to- 

 gether for convenience, since they are insoluble in water and 

 most protein solvents, and are constituents of protective or sup- 

 porting portions of the body. Keratin is the chief constituent 

 of hair, horn, nails, feathers, the epidermal layer of the skin, 

 etc. A keratin also has been obtained from the brain and nerve 

 tissue. There probably are several keratins. The keratins con- 

 tain much sulphur (1-5%). They give the characteristic protein 

 color tests. 



Collagen is the chief constituent of the connective tissue and 



