44 



A TEXTBOOK OF PHYSIOLOGY 



In the following table will be seen the varying yields of the different 

 amino acids obtained from 100 parts of various proteins, after complete 

 hydrolysis with h\*drochloric or sulphuric acid. Tyrosin and cystin 

 are separated by crystallization, after neutralizing and concentrating 

 the liquid. The diamino acids arginin, lysin, and the allied body 

 histidin are separated from the rest of the products by being pre- 

 cipitated by phosphotungstic acid in acid solution. Tryptophan is 

 separated by precipitation by mercuric sulphate in the presence of 

 5 per cent, sulphuric acid after tryptic digestion. The other amino 

 acids are separated after hydrolysis of protein by hydrochloric acid 

 by fractional distillation of their ethereal salts under greatly reduced 

 pressure. It will be noticed that the figures given do not by any means 

 add up to 100 per cent. This is due to the occurrence of feome in- 

 evitable loss in the method of separation, and to the fact that, doubt- 

 less, all the components of protein have not yet been isolated. 



