NUTRITION OF BACTERIA. 31 



therefore, have their carbon and nitrogen presented 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 degree, 

 but by no means so easily, from salts of ammonia. In 

 some of Nageli's experiments it appeared probable that 

 they could obtain the necessary amount of nitrogen 

 from salts of nitric acid. At all events, he was able 

 in certain cases to demonstrate a reduction of nitric to 

 nitrous acid, and ultimately to ammonia. Nevertheless, 

 in all of these experiments circumstances point to the 

 probability that the nitrogen obtaiued by the bacteria 

 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 be borne in mind, however, that 

 there exists a specific group of bacteria, the nitrifying 

 bacteria, that apparently increase and multiply without 

 having access to proteid .nutrition. They are concerned 

 in the particular form of fermentation that results in the 

 oxidation of ammonia to nitrous and nitric acids, a pro- 

 cess 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 glyce- 

 rine and many of the fatty acids; and from the alkaline 

 salts of tartaric, citric, malic, lactic, and acetic acids. 

 In some instances carbon compounds, which when 

 present in concentrated form inhibit the growth of bac- 

 teria, may, when highly diluted, serve as nutrition for 



