FAEMYAED MANUEE 317 



most part, insoluble and more complex than those of the 

 urine, and they undergo fermentation much more slowly. 

 They consist mainly of albuminoids, the decomposition 

 of which by bacterial action has been previously alluded 

 to. It was shown (p. 154) that they pass through a 

 series of complex changes, the nitrogen being converted 

 into amino-acid bodies and finally into ammonia. 



The nitrogenous matter of the litter ultimately suffers 

 a like fate, the change taking place more or less readily 

 according to the nature of the substance. In wheat 

 straw about a fifth part oi the nitrogenous matter is 

 digestible, and it is to be supposed that this part is 

 more readily attacked by the microbes than the remainder, 

 and also more readily than the nitrogenous matter of the 

 dung, which, it will be remembered, consists of the 

 indigestible portions of the food. 



The Fate of the Ammonia. The conversion of the 

 nitrogen into ammonium carbonate may be regarded as 

 the completion of the first stage, but it is subject to 

 further changes which materially affect the character of 

 the manure. A certain amount of ammonium compounds 

 is nearly always present as they are continually being 

 formed, but they do not accumulate as might be expected. 

 The largest amount is produced during the initial stages 

 of fermentation ; the quantity rises to a maximum and 

 then diminishes again. The longer the manure is kept 

 the smaller is the proportion of ammonium compounds 

 generally found. It is obviously a matter of importance 

 to follow them up and see what becomes of them. 



Under certain conditions which are not well defined, 

 some of the nitrogen is liberated in the free state. 

 The phenomenon is called denitrification, but it is not 

 clear whether it is due to the formation and subse- 

 quent reduction of nitric acid or to the direct oxidation 

 of the hydrogen of the ammonia. In either case it can 



