AMMONIACAL FERMENTATION OF URINE 217 



explained. Of these the following are the most 

 important : 



(i) The ammoniacal fermentations of urea and 

 allied nitrogenous compounds present in the 

 liquid excreta. 



(ii) The breaking down of the proteins in the 

 putrefactive process (see pp. 100-103). 



(iii) Nitrification and denitrification (see pp. 134-160). 



(iv) The fermentation of cellulose. 



(i) The Ammoniacal Fermentation of Urine. 

 Freshly excreted urine of man is slightly acid due to 

 the presence in it of acid sodium phosphate, that of 

 most herbivorous animals being neutral or slightly 

 alkaline. However, on being exposed to the air for a 

 few hours the urine of all animals becomes very strongly 

 alkaline and develops an odour of ammonia, which is 

 often prevalent in stables. The urea, uric and hippuric 

 acids, also undergo fermentation with the production of 

 ammonium carbonate, from which gaseous ammonia is 

 set free. In the case of urea the change is one of 

 hydrolysis, thus : 



CO(NH 2 ) 2 + 2H 2 O = (NH 4 ) 2 CO 3 



Urea Ammonium Carbonate 



A number of different species usually spoken of as " uro- 

 bacteria " are capable of effecting this change. They 

 are very widely distributed in the air, in dirty water, in 

 dust and soil, and in manure heaps. Some of them are 

 coccus forms while others are bacilli : the latter appear 

 to prevail in soil. All are aerobic, and grow best at a 

 temperature of 30 to 32 C. in 2 to 5 per cent, solutions 

 of urea made slightly alkaline by adding .2 per cent, of 



