Carbon and Nitrogen ,'W 



tot irs. Pathogenic bacteria, in particular, seem to re- 

 quire protein compounds MS their source of carbon, :nil 

 .some specie's will not. develop without' it. 



Cenerally speaking, therefore, different species of 



bacteria are not alike' in their preference for one or 

 another source of carbon. Some species will develop in 

 solutions of cane-sugar fully MS well MS in solutions of 

 grape sugar, while others will grow in solutions of 

 grape-sugar, hut not in solutions of cane -sugar. Analo- 

 gous relations may bo observed in the ease of other 

 sugars. Again, there are species, like certain kinds of 

 denit rif\ in;; bacteria, which will develop perfectly in 

 culture solutions cunt Mining salts of citric acid MS the 

 only source* of carbon, while other organisms will not 

 grow in such solution- ai all. Similarly, there are bac- 

 teria that will utilize pure cellulose, when the vast 

 majority of microorganisms will utterly fail to develop. 

 These examples will snllice to show that (hero are deep 

 seated differences in the chemical machinery of the 

 bacterial cells and in the methods by which the carbon 

 compounds are transformed and assimilated. 



The source nj nitrogen. Relations like those ju;( 

 described exist also in the assimilation of nitrogen food 

 by bacteria. Just as in t he case of field crops, some plants 

 prefer ammonia and others nitrate, as a source of 

 nitrogen, so among bacteria, different species show 

 analogous preferences. Certain specie's reject both am- 

 monia and nitrate nilrouen. and demand for their 

 .UTuwth some organic nitrogenous compound (prefer- 

 ably protein), or substances derived from protein and 

 known as amino-compounds. The so-called nitrogen- 



