786 BACTERIA : THEIR WORK 



The particular species of bacteria concerned in the marsh- 

 gas fermentation of cellulose are not yet known with any 

 degree of certainty. Some of them appear to be allied to 

 the butyric bacteria. Omelianski isolated from river mud 

 and horse dung an anaerobic slightly curved bacillus which 

 fermented cellulose with the production of methane and carbon 

 dioxide. 



7. Fermentation of Urea. — By far the largest part of the 

 waste nitrogen which leaves the body of an animal passes out in 

 the form of urea or carbamide, CO(NH2)2, dissolved in urine. 

 The latter on keeping a few hours, gradually becomes more and 

 more alkaline and develops an ammoniacal odour, the urea in it 

 being hydrolysed into ammonium carbonate according to the 

 following reaction : — 



CO(NH2)2 + 2H2O = (NHJ,C03. 



As the carbonates of ammonia are volatile and readily suffer 

 partial decomposition into carbon dioxide and ammonia, con- 

 siderable loss of nitrogen takes place from a manure heap in 

 which this fermentation is going on : the loss begins in the stable, 

 and to prevent it either wholly or in part, the use of absorbent 

 peat litter in the stalls or the addition of superphosphate of 

 lime to the manure are useful. 



The change of urea into ammonium carbonate is brought 

 about by a number of distinct species of bacteria which are 

 found abundantly distributed in soils, drainage and river water, 

 manure heaps and sewage. 



Some of the organisms are bacilli, others cocci or sarcinx; 

 a small amount of free acid stops the development of all of 

 them. 



According to Miquel the hydrolysis of urea is not effected 

 directly by the bacteria themselves, but by an enzyme, urease, 

 which they secrete; the enzyme has been obtained pure by 



