RELATION TO ENVIRONMENT CLASSIFICATION 31 



anaerobic environment. Fe'rran 11 succeeded in adapting the tetanus 

 bacillus to an aerobic environment. In this case, however, the viru- 

 lence of the bacillus was lost. 



Nitrogen. The nitrogen required by bacteria is taken, in most 

 cases, from proteins, and many of the non-diffusible albumins may be 

 rendered assimilable by the proteolyzing enzymes possessed by micro- 

 organisms. Among the pathogenic, more strictly parasitic bacteria, 

 moreover, a delicate specialization may be observed as to the partic- 

 ular varieties of animal albumin which may be utilized by them. 

 Thus the gonococcus grows more readily only upon uncoagulated 

 human blood serum, and the diphtheria bacillus outgrows other bac- 

 teria upon a medium composed for the greater part of coagulated 

 beef serum. For bacteria that do not require native animal protein 

 for their development, the most common nitrogenous ingredient of 

 culture media is peptone. 



Many bacteria (pathogenic and saprophytic), on the other hand, 

 may thrive on media containing absolutely no protein, in which case, 

 of course, a synthesis of protein must be assumed. A medium used 

 to demonstrate this, devised by Uschinski, 12 contains ammonium lac- 

 tate, glycerin, asparagin (the amine of anino-succinic acid), and 

 inorganic salts. 



Creatin, creatinin, urea and urates, and even ammonia compounds 

 and nitrates, may serve as sources of nitrogen for many of the less 

 parasitic bacteria. A limited number of species, moreover, the 

 bacilli in the root tubercles of the leguminosae and the nitrogen- 

 fixing organisms of the soil, can obtain their nitrogen directly from 

 the free N 2 of the atmosphere. 



Although the sources of carbonaceous and of nitrogenous food 

 have been separately discussed, it should not be forgotten that, in 

 many instances, both elements are taken up within the same com- 

 pound, and that separate supplies are a necessity in isolated cases 

 only. 



Hydrogen. Hydrogen is obtained by bacteria largely in combi- 

 nation as water and together with the carbon and nitrogen contain- 

 ing substances. 



Salts. The phosphatic constituents of the bacterial body are 

 taken in, chiefly, as phosphates of magnesium, calcium, sodium, or 



11 Ferran, Cent, f . Bakt., I, xxiv, 1898. 



12 UschinsTci, Cent, f . Bakt., I, xiv, 1893. 



