NUTRITION OF BAOTEBTA. 31 



the other hand, owing to the absence of chlorophyll 

 from their tissues, do not possess this power. Tliey 

 must, therefore, have their carbon and nitrogen pre- 

 sented as such, in the form of decomposable organic 

 substances. 



In general, the bacteria obtain their nitrogen most 

 readily from soluble albumins, and, to a certain extent, 

 but ) ly no means so easily, from salts of ammonium. In 

 some of Nageli' s experiments it appeared probable that 

 they could obtain the necessary amount of nitrogen 

 from inorganic nitrates. At all events, he was able 

 in certain cases to demonstrate a reduction of nitric to 

 nitrous acid, and ultimately to ammonia. Neverthe- 

 less, in all of these experiments circumstances point to 

 the probability that the nitrogen obtained 1jy the bac- 

 teria for building up their tissues in the course of their 

 development was derived from some source other than 

 that of the nitric acid or the nitrates, and that the 

 reduction of this acid was most probably a secondary 

 phenomenon. It must lie borne in mind, however, tliat 

 there exists a specific group of bacteria, the nitrifying 

 bacteria, that apparently increase and multiply without 

 appropriating proteid nutrition. They are concerned 

 in the particular form of fermentation that results in 

 the oxidation of ammonia to nitrous and nitric acids, a 

 process everywhere in progress in the superficial layers 

 of the soil. 



For the supply of carbon many of the carbon com- 

 pounds serve as sources upon which the bacteria can 

 draw. The carbon deficit, for example, can be obtained 

 from sugar and bodies of like composition; from gly- 

 cerine and many of the fatty acids; and from the alka- 

 line salts of tartaric, citric, malic, lactic, and acetic 



