NUTRITION OF BACTERIA. 81 



fore, 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 obtained 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. 



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 obta,ined 

 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 pres- 

 ent in concentrated form inhibit the growth of bac- 

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

 them. Salicylic acid and ethyl alcohol come under this 

 head. 



In addition to carbon and nitrogen, water is essential 

 to the life and development of bacteria. Without it 

 no development occurs, and in many cases drying the 

 organisms results in their death. Certain forms, on the 

 contrary, though incapable of multiplying when in the 



