88 A. I. RINGER 



. 

 2. Cystein or a-amino p-thio-propionic acid. 



a-CIINH 2 



COOII 

 3. Cvstin or dicystein. 



CIL s s CIL, 



o ciixn 2 



I I 



COOII COOII 



These three substances are neutral in reaction, and have properties sim- 

 ilar to those in group "A". The two latter are the only amino acids which 

 contain sulphur, and there is every indication to prove that only the latter 

 exists in protein and that the former is only a product of its hydrolysis. 

 4. (3-IIydroxyglutamic acid, Dakin (1918, 1919)* 

 COOII 



CH 2 



I 

 P-CHOH . 



COOH 



This acid is similar to the dibasic acid glutamic acid, except that it 

 lias an hydroxyl radical attached to the p-carbon. This is the youngest 

 member of the amino acid family, having been discovered by H. D. Dakin 



in 1918. 



D. Diamino acids. 



1. Lysin or a-e-diamino caproic acid. 



8-CH 2 



I 

 Y-CH 2 



a-CHNII, 



I 

 COOH 



