52 BIOLOGY AND TECHNIQUE 



tidine. Some light seems to have been shed on the mechanism of 

 this process of decarboxylizatioii by Koessler and Hanke,* 5 who 

 found, while investigating the production of histamine by B. coli, 

 that it was formed only in cultures in which considerable quantities 

 of acid were being produced at the same time, and they believe 

 that the production of this strongly basic substance offsets to a 

 degree the acid production and enables the organisms to develop 

 further before the H-ion concentration reaches the point of inhibi- 

 tion. Sepsine, another base of unknown composition, but probably 

 related in structure to the other ptomaines, has been isolated by 

 Faust from putrid yeast, and has been shown to be highly toxic. 



In breaking down animal excreta, the task of the bacteria is 

 rather a simpler one than when dealing with the cadavers them- 

 selves, for here a part of the cleavage has already been carried out 

 either by the destructive processes accompanying metabolism, or by 

 partial decomposition by bacteria begun within the digestive tract. 

 This material outside of the body is further reduced by bacterial 

 enzymes into still simpler substances, the nitrogen usually being 

 liberated in the form of ammonia. One example of such an am- 

 moniacal fermentation may be found in the case of the urea fermen- 

 tation by Micrococcus urea?, in which the cleavage of the urea takes 

 place by hydrolysis according to the following formula: 



(NH,) 2 CO + 2H, = C0 2 + 2NH 3 + H 2 



Similar ammoniacal fermentations are carried out, though perhaps 

 according to less simple formulae, by a large number of microor- 

 ganisms. Perhaps the most common species which possesses the 

 power is the group represented by B. proteus vulgaris (Hauser). 



From what has been said it follows naturally that, so far, the 

 decomposition of the protein molecule from its complex structure 

 to ammonia or simple ammonia compounds is an indispensably im- 

 portant function, not only for agriculture, but for the maintenance 

 of all life processes. It is clear, on the other hand, that a further 

 decomposition of ammonia compounds into forms too simple to be 

 utilized by the green plants would be a decidedly harmful activity. 

 And yet this is brought about by the so-called denitrifying bacteria 

 which will be considered in a subsequent section. 



8 Koessler and HanTce, J. Biol. Chem., 1919, 39, 539. 



