GENERAL FUNCTIONS OF MICROBES 9 



by distillation. The problem of the origin of coal has therefore 

 some relation to the problem of the origin of petroleum. The 

 decomposition of fatty substances commences with their 

 saponification, which splits them into fatty acids and glycerine, 

 and glycerine is a good food medium for various bacteria. 



The moulds decompose fatty acids into carbonic acid and 

 water. Fats resist decomposition longer than other carbo- 

 hydrates, and longer than nitrogenous substances ; it is 

 from this cause that the proportion of fat increases in a cheese 

 which has been kept, or in a dead body which is decomposing. 

 The ' adipocere ' is the final stage in an animal body left entirely 

 to nature. 



III. Putrefaction of albuminous materials. 



Putrefaction returns to the soil the nitrogen which 

 makes up 1 5 per cent, of the proteins of animal tissues. 



Since plants draw their nitrogen from the soil in the form of 

 nitrates and salts of ammonia, it is necessary for the complex 

 protein molecule to be broken down so as to supply finally 



§ 88 



- ,., 00 



Cb (9 



Fig. 2. — Ammoniacal fermentation Fig. T,. — Urobacillus oi 



of urine : Urocococcus of Pasteur. Duclaux. 



nitrogen in the form of ammonia and nitric acid. Later 

 green plants and finally animals, raise this mineral nitrogen to 

 the level of organic nitrogen. 



Already during life animals discharge nitrogen with their 

 excretions in the form of urea, uric acid and hippuric acid. 

 The Urobacteria (ther^ are about a hundred species known) 



