74 THE CHEMISTRY OF CATTLE FEEDING 



coagulated and it is independent of the presence of calcium 

 salts. 



G-lutelins and Gliadins. The elastic, glue-like mass 

 which gives the toughness or " strength " to dough, and which 

 can be obtained from wheat flour by removal of the starch, 

 was formerly called gluten. When separated from adventitious 

 impurities, e.g. starch, fat, etc., this substance is found to con- 

 sist of a mixture of proteins of which the most important are 

 now called glutelin and gliadin, or wheat-glutelin and wheat- 

 gliadin to distinguish them from similar compounds in other 

 cereals. The gliadins are insoluble in water, but are soluble 

 in alcohol of 70 to 80 per cent, strength. The glutelins are 

 insoluble in water and in alcohol, but are very readily soluble 

 in dilute acids and alkalis. The gliadin of oats has been 

 called avenin ; that of maize, zein ; that of barley, hordein, 

 and so on. 



Phospho-proteins. As the name implies, the members of 

 this group contain atoms of phosphorus in the molecule, and 

 they exhibit a marked acid reaction. They are insoluble in 

 water, but readily form salts with alkalis and ammonia which 

 are soluble in water and are not coagulated on boiling. Being 

 insoluble, the phospho-proteins are precipitated from solutions 

 of their salts on addition of acids. If the quantity of acid is 

 just sufficient to acidify the solution, but not enough to cause 

 precipitation, the phospho-protein coagulates on warming. 



Three stages can be recognised in the reaction which takes 

 place when phospho-proteins are treated with pepsin in the 

 presence of hydrochloric acid. First, the protein is dissolved 

 and partially converted into proteose. Second, a radicle 

 containing phosphorus is split off. Third, the phosphorus 

 containing radicle is dissolved while the peptonisation of the 

 remainder proceeds. The portion which contains the 

 phosphorus has a marked acid character, and is readily 

 soluble in alkalis. It has unfortunately been called " para- 

 nucleic acid," but it has no connection with nuclein (p. 79). 

 The paranucleic acid is precipitated from its alkali solutions 

 by acids. It readily dissociates into acid albumin, albumose, 

 and phosphoric acid. 



