EVOLUTION OF PROTEIDS 75 



acetic acid or to normal caproic acid ; and so the 

 aliphatic or fatty-acid series comes into the con- 

 struction of the amino-acids and proteins. The im- 

 portance of these amino-acids in the construction of 

 protein is evident, for asparagine and phenyl- 

 alanine occur in most animal and vegetable pro- 

 teids ; tyrosin and prolin in all animal proteids ; 

 glycocoll forms 25 percent, of elastin and 1 of edestin; 

 leucinc forms 10 per cent, of casein, 20 of serum- 

 albumin, 15 of fibrin, 21 of elastin, and 29 of haemo- 

 globin ; and glutaminic acid forms 30 per cent, of 

 gliadin, 8 of egg-albumin, 10 of casein, and 8 of 

 serum-globulin. 



The occurrence of protein substances which con- 

 tain a carbohydrate group has been known for some 

 time. It is always an amino-sugar, and usually 

 glucosamine, united to the protein in a glucoside-like 

 combination. It has also been shown by Pavy and 

 others that true proteids yield a carbohydrate on 

 hydrolytic cleavage. A small amount of such carbo- 

 hydrate has been separated from yolk-proteids, ovo- 

 globulin, serum-globulin, paraglobulin, fibrin, serum- 

 albumin, and albumin of the Graminacese. All pro- 

 teids do not contain a carbohydrate group, for none 

 has been obtained from casein, myosin, fibrinogen, 

 ovo-vitellin, and some vegetable proteids. It is also 

 at present undecided as to whether the carbohydrate 

 group positively belongs to the proteid molecule or 

 is to be regarded as an impurity.* 



The albumins are very sparingly present in vege- 

 tables, but globulins are very common. They con- 

 tain vegetable-myosin, which is believed to be the 



* Hainmarsfcen's "Physiological Chemistry," p. 23. 



