NUTRITION OF BACTERIA. 25 



Just what their exact role in nature is, it is difficult to 

 say ; but it is probable that in addition to their most 

 conspicuous function of color production, they are also in 

 some way concerned in the great process of disintegra- 

 tion which is constantly going on in all dead organic 

 substances. 



We know that through the agency of chlorophyll, in 

 the presence of sunlight, the green plants are enabled to 

 obtain the amount of nitrogen and carbon which is neces- 

 sary to their growth from such simple bodies as carbon 

 dioxide and ammonia, which they decompose into their 

 elementary constituents. The bacteria, on the other 

 hand, owing to the absence of chlorophyll from their 

 tissues, do not possess this power. They must have 

 their carbon and nitrogen presented as such, in the 

 form of decomposable organic compounds. 



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 

 the 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. Neverthe- 

 less, 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 devel- 

 opment, was derived from some source other than that of 

 the nitric acid or the nitrites, 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 obtained 



