Chemical Constituents of the Animal Body. 221 



by the hydrolysis of a given protein. The latter could 

 then be differentiated from other members of the class by 

 the quality and quantity of the ammo-acids derived by 

 hydrolysis. In the following list it will be observed that 

 some of the amino-acids are aliphatic derivatives, whereas 

 others are aromatic. Others again contain rings other 

 than the benzene ring, such as the iminazol, the pyrol- 

 lidine, and the indole rings. It would be extending the 

 limits of this book too far to enter into detail into the 

 chemistry of all the amino-acids. It will be obvious that 

 the substances with the simpler formulae are just amino- 

 derivatives of the fatty acids, with the amino group in 

 the a position. All the substances in the undermentioned 

 list have been obtained synthetically, and there is no 

 doubt as to their chemical constitution. In addition to 

 those given, other amino-acids have been recently described 

 which have been obtained in small quantities by the 

 hydrolysis of certain proteins. Their production as 

 hydrolysis products has not, however, been in all cases 

 definitely established, and they are omitted from the 

 following list : 



HYDROLYSIS PRODUCTS OF PROTEINS. 



A. Monoamino-monocarboxylic Acids. 



1. Glycine, a-aminoacetic acid, (NH 2 )CH 2 -COOH 



2. Alanine, a-aminopropionic acid, CH 3 -CH(NH 2 ) COOH 



3. Valine, a-aminoisovaleric acid 



CH CH(NH 2 ) COOH 



4. Leucine, a-aminoisocaproic acid 



CH 3X 



>CH CH, CH(NH 2 ) COOH 

 CH/ 



