PRODUCTS OF MICROBIAL ACTIVITIES 241 



e.g., in the clearing of milk or the gelatin liquefaction, meaning that the 

 insoluble protein has been made soluble. 



The amino-acids are the first well known compounds of protein de- 

 composition. They are organic acids, in which a hydrogen atom is 

 substituted by a NH 2 radical. Some of them are simple compounds, 

 as the amino-acetic acid NH 2 CH 2 COOH and also the amino-capronic 

 acid usually called leucin (CH 3 ) 2 CH CH 2 CH(NH 2 ) COOH. Others 

 are of a more complex nature, such as the tyrosin or hydroxy-phenyl- 

 aminopropionic acid, C 6 H 4 (OH) CH 2 CH (NH 2 ) COOH, and the 

 tryptophan or indol-amino-propionic acid, C 8 H 6 N CH 2 CH(NH 2 ) 

 COOH. 



Of other nitrogenous products which are not amino-acids, a few 

 are of striking significance. The very disagreeable odor of putrefying 

 proteins and of excreta is due to indol (C 8 H 7 N) and methyl-indol or 

 skatol (C 8 H 6 N-CH 3 ). Indol gives a rose color with nitrites in acid 

 solution, and this convenient reagent is used in the identification of 

 bacteria. Another group are the amins. The simplest amins are 

 the methyl-amins, of which the tri-methylamin (CH 3 ) 3 N is produced 

 by several bacteria. The fishy odor of the brine of salted herring is 

 largely due to this compound. In this group belong also a large number 

 of the so-called ptomains. 



The ptomains (page 592) are alkaloid-like bodies of basic character 

 and of more or less well-known structure. Some of them are notorious 

 for being very strong poisons, while others are quite harmless. These 

 bodies are called ptomains because they were first discovered in 

 putrefying corpses. The best-known compounds of this character 

 are the putrescin or tetra-methylen diamin [NH 2 (CH 2 )4NH 2 ] and the 

 cadaverin or penta-methylen-diamin [NH 2 (CH 2 ) 5 NH 2 ], which can 

 scarcely be considered poisonous. The methyl-guanidin 



NH 2 

 HN = C<^ 



NHCH 3 



may be mentioned as an example of a very poisonous ptomain. Another 

 poisonous ptomain is the neurin CH 2 = CH N(CH 3 ) 3 OH which has 

 been found frequently as a product of putrefaction. 



Ammonia is the end product of protein decomposition, as far as 



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