THE CONSTRUCTION OF PKOTEINS 169 



Neither peptones nor proteoses occur very plentifully 

 in plants, and they are probably formed in them only from 

 the decomposition of the more stable forms of globulin and 

 albumin. There is no evidence at present that they are 

 stages in the constructive process. 



Some of the proteoses occur in certain seeds in associa- 

 tion with some of the globulins. Both the albumins and 

 the globulins, and probably the meta-proteins as well, are 

 transformed into proteoses and peptones by the action of 

 hydrolysing agents, such as dilute mineral acids and certain 

 secretions of the protoplasm known as enzymes, whose 

 action will be treated of in a subsequent chapter. 



Besides these classes of proteins, another occurs, the 

 members of which present the curious peculiarity of being 

 soluble in alcohol. Proteins of this group have been extracted 

 from the endosperm of some of the cereal grasses. Examples 

 of them are found in the zein of maize, and the gliadin and 

 glutenin of wheat flour. Zein differs from the crystallised 

 protein of the hemp in its comparatively low content of 

 nitrogen, which amounts to only 16'13 per cent.- It dissolves 

 easily in alcohol of about -820 specific gravity, but is 

 insoluble in absolute alcohol. It is insoluble also in water, 

 but in mixtures of alcohol and water it dissolves to a greater 

 or less extent, being most easily soluble in a mixture con- 

 taining about 90 per cent, of the spirit. In one of a lower 

 concentration than 50 per cent, it is very sparingly soluble. 

 Zein can be dissolved by glycerine if heated to 150 C. ; 

 also by glacial acetic acid and by dilute solutions of caustic 

 potash. Like other proteins, it is converted into peptone 

 by peptase and hydrochloric acid. 



The original construction of protein matter, like that 

 of carbohydrates, seems to be carried out only by 

 vegetable protoplasm. It does not, however, appear to be 

 dependent upon the same conditions as the process already 

 described. It cannot be classed with the latter as a process 

 of photosynthesis, and it is only indirectly dependent 

 upon the action of the chlorophyll apparatus. Unlike the 



