28 BIOLOGY AND TECHNIQUE 



induced to grow in indifferently anaerobic environment. Ferran, * 

 succeeded in adapting the tetanus bacillus to an aerobic environment. 

 In this case, however, the virulence 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 microorganisms. 

 Among the pathogenic, more strictly parasitic bacteria, moreover, a 

 delicate specialization may be observed as to the particular varieties of 

 animal albumin which may be utilized by them. Thus the gonococcus 

 grows more readily only upon uncoagulated human blood serum; the 

 Pfeiffer bacillus requires hemoglobin, and the diphtheria bacillus out- 

 grows other bacteria 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 pepton. 



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, 2 contains ammonium lactate, 

 glycerin, asparagin (the amide of amido-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 organ- 

 isms of the soil, can obtain their nitrogen directly from the free N2 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 compound, and 

 that separate supplies are a necessity in isolated cases only. 



Hydrogen. Hydrogen is obtained by bacteria largely in combina- 

 tion as water and together with the carbon and nitrogen containing 

 substances. 



Salts. The phosphatic constituents of the bacterial body are taken 

 in, chiefly, as phosphates of magnesium, calcium, sodium, or potassium. 

 The phosphates seem to be necessary constituents of culture media, 



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



2 Uschinski, Cent. f. Bakt., I, xiv, 1893. 



