THE BIO-CHEMISTRY OF ANIMALS AND PLANTS 693 



relationships will produce an important change in our present 

 classification. With regard to the vegetable proteins, this is 

 all the more desirable, as they can only be fitted in with 

 difficulty into the present system. A complete up-to-date 

 treatise ^ of the vegetable proteins has still to be written, and 

 their nomenclature and classification are at present in a most 

 unsatisfactory and perplexing state. For the purpose of this 

 paper the material to be dealt with has been divided into four 

 main classes, it being recognised, however, that this classification 

 can only be a tentative one, and open to criticism. 

 The following classes are proposed : 



1. Phyto-albumins. 



2. Phyto-globulins. 



3. Gliadins (alcohol-soluble proteins). 



4. Phyto-caseins (phyto-vitellins).^ 



I. The proteins of the first class are the least known of 

 vegetable proteins, the reason for this being that the seeds, 

 which form the main source for the study of plant proteins, 

 contain albumins only in relatively small proportions. Many 

 observations show, however, that they are also present in leaves 

 and the cell-sap of other parts of plants. 



The vegetable albumins possess the same characteristics 

 as those of animal origin. They are soluble in water and salted 

 out by ammonium sulphate and other salts. They require a 

 larger amount of salt for their precipitation than the globulins. 

 They may be separated from the latter by dialysis, remaining 

 in solution after the removal of the salts. They have not yet 

 been obtained in a crystalline form, are coagulated by heat, and 

 show all the typical colour reactions of the proteins. They 

 are phosphorus-free. 



The best known of the vegetable albumins is a substance 

 called leucosin. It occurs in small quantities in grasses, but 

 has been prepared mainly from wheat grains (also rye, barley, 

 and maize), in which seeds it is present to the extent of 0*3 — 0*4 



^ Only two exhaustive treatises exist on vegetable proteins : Die Eiweisskorper 

 der Getreidcarien, etc., Ritthausen, 1872 ; and Die Proteide der Getreidearten, 

 etc., Griessmayer, 1887. The latter is a translation of Chittenden and Osborne's 

 collected older papers. 



^ The name " Glutelin " has recently been proposed by a committee of the 

 American Physiological Society for these substances. 



