THE PROTEIN SUBSTANCES. 77 



behavior and is a common product of protein decomposition. 

 Slightly soluble in water and has a sweetish taste. 



AMINO PROPIONIC ACID, OR ALANINE, C 3 H 7 NO 2 . This is 

 in a sense the nucleus substance corresponding to tyrosine and 

 phenylalanine just referred to. It is a soluble product rather 

 widely distributed in protein bodies. 



AMINO VALERIC ACID, CgH^NOg. This substance is ap- 

 parently the a product. It is usually mixed with leucine and 

 is separated only with difficulty from this body. 



a-PYRROLIDINE CARBOXYLIC ACID, C 5 H 9 NO 2 , (C 4 H 7 .NH 



COOH). From the conditions under which it has been found 

 this interesting body is supposed to be a primary product. It 

 is an imino not an amino derivative. It was first obtained 

 from casein and later from other proteins. The closely 

 related hydroxy-a-pyrrolidine carboxylic acid has been ob- 

 tained from gelatin. 



From the above list it will be seen that the amino acids 

 predominate; most of them, possibly all, are the a compounds, 

 and as will be shown below, they make up a very large portion 

 of the whole protein molecule. 



GLUCOSAMINE, C 6 H 11 O 5 (NH 2 ). This appears to be an 

 important constituent in some groups of protein bodies. It 

 has been obtained in quantity from the glucoproteids and is 

 possibly present in small amount in all. It is usually obtained 

 as a salt, hydrochloride or hydrobromide, which is readily sol- 

 uble in \vater and optically active. 



AMMONIA, NH 3 . This is always found in relatively large 

 amount. 



SULPHUR COMPOUNDS. Hydrogen sulphide, ethyl sulphide, 

 thiolactic acid, C 3 H 6 SO 2 , cystin, C 6 H 12 N 2 S 2 O 4 , and traces of 

 other bodies which contain sulphur have been identified in 

 small amount among the decomposition products. 



CARBONIC ACID is apparently a constant derivative, but may 

 appear as a result of some secondary reaction. Its significance, 

 therefore, is obscure. 



AYith acids other than hydrochloric very similar reaction 



