196 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



COOH 





CH 



or 



-N 



1 

 H 



a- CH 2 . CH(NH 2 ) COOH 



H 



In this way we can see how indol may be produced by the 

 decomposition of albumin substances. It is of interest to note 

 that the formation of indol, recognised by the red coloration 

 it produces with nitrous acid, is a characteristic reaction for 

 certain bacteria, notably B. coli, and serves to distinguish this 

 from the more dangerous typhoid bacillus. The cholera-red 

 reaction given by the cholera organism depends also on the 

 formation of indol. 



In both cases the red coloration is due to the formation 



CH 



of nitroso-indol, 



! N-NO 



formed by the action of 



nitrous acid on the imino group present. 



3. Amino - valerianic acid, CH 3 CH 2 CHoCHNH 2 COOH. 

 This acid is of interest mainly on account of its derivatives, 

 the chief of which is known as arginin, to which reference 

 will be made later, and leucin or isobutyl-a-amino-acetic acid, 

 which has the following formula : 



