60 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS 
upon three factors: (1) The substance which is decaying; (2) the 
species of bacteria which produces the decay; (3) the conditions 
under which the decay occurs. 
The Ammoniacal Fermentation.—One phase of these decom- 
position processes must be especially mentioned. After passing 
through an unknown series of intermediate stages, the nitrogen 
of the decaying mass assumes, in large part, the condition of 
ammonia. One of the first and easiest substances to undergo 
this ammoniacal fermentation is urea. Urine is always filled 
with bacteria, even while in the ducts from the bladder, and among 
them are several species that cause it to break down to form am- 
monia. 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 pos- 
sible. 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. 16), 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 under- 
stood. 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 peplonizing bacteria, they are converted into pepione-like 
bodies which are simpler than ordinary proteids. ‘These are 
further reduced into amino acids, and the latter finally converted 
into ammonia, which is quite likely to unite at once with carbonic 
dioxid, that is also being liberated, to form carbonate of ammonia 
