24 INTRODDCTORY— THE CONSTITUENTS OF MILK. 



/3-phenyl-a-amino-propionic acid, or phenyl- alanine. 

 )3-io-oxy-plienyl-a-amino-propionio acid, or tyrosine. 

 Indole-amino-propionic acid, or tryptophane. 

 This has the constitution 



G. Hydroxy-diamino-mono-carboxylio acid. 

 Tri-hydroxy-diamino-dodecanoio acid. 



H. Diamino-di-carboxylio acids. 



Diamino-glutario acid. 



Diamino-adipic acid. 

 I. Hydroxy-diamino-di-carboxylic acids. 



Hydroxy-diamino-sebacic acid. 



Dihydroxy-diamino-suberio acid, and probably others. 



J. Pyrrolidine compounds. 



a-pyrrolidine-carboxylic acid, or proline. 

 Oxy-pyrrolidine-carboxylic acid, or oxy-proline. 



Proline has the constitution 



CHa— CH2 



I I 



CH, CH COOH 



"V 

 NH 

 K. Thio-amino-acids. 



Protein-cystine and stone-oystine. 

 These are derived respectively from. 

 (i-amino-)3-thio-lactic acid, and 



u-thio-fj-amino-lactic acid, and are represented by the following 

 constitutions : — 



Prntein Cystine. Stone Cystine. 



S — S NH, NH2 



II II 



CH2 CH2 CH2 CH, 



I I I 



NH,— CH CH— NH, CH— S— S— CH 



' I I " i I 



COOH COOH COOH COOH. 



Among other compounds obtained by the hydrolysis of proteins are : — 

 *L. Purine bases. These are contained in the nucleo-proteins ; they are 

 products contauiing a pyrimidine and a glyoxaline (or imidazolyl) ring, 



thus — 



PyriniiOine. Glyoxaline. Pniine. 



IN = *CH 'N = "CH 



II I J 



i'CH i^CH CH— NH^ ^CH '^C— 'NH^ 



II II II >CH. 11 II >CH 



'N — «CH C — N ^^—^C — "N 



* It is not certain whether purine or pyrimidine derivatives occur in 

 mUk proteins. 



