54 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS. 



(Fig. 1 6). Most of these bacteria produce this action through an 

 enzyme that they secrete, named urase. Under proper conditions, 

 as much as 97 per cent, of the nitrogen in the urea is converted into 

 ammonia in a space of four days. The ammonia is a volatile 

 product and has, consequently, a tendency to pass off into the air, 

 as may readily be recognized from the odor of ammonia that is 

 frequently perceived around a manure pile. This represents a per- 

 manent loss of nitrogen, and should be avoided as much as possible. 



FIG. 1 6. Various bacteria causing the ammoniacal fermentation of urea (Beijerincti). 



The loss is greater when the liquid is concentrated, and consequently 

 less if the urine can be poured upon the soil at once, than if stored 

 in vats or even mixed with solid manure. 



Although urea shows the ammoniacal fermentation most readily, 

 other nitrogenous bodies, like proteids, etc., also may give rise to 

 ammonia (Fig. 17), which is, indeed, one of the common end-products 

 of proteid decomposition. The chemical changes that occur in 

 proteid decomposition are complex and not wholly understood. 

 The first step seems to be quite like that taken when they are 

 digested in the digestive tract of animals, for, under the action of the 



