172 PHYSIOLOGY OF BACTERIA 



or more amino-acids, because they cannot form one from 

 the other. In this connection it should be mentioned 

 that Abderhalden and Rona found no influence of the 

 source of nitrogen upon the composition of the protein 

 of Aspergillus niger; whether potassium nitrate, glycocoll 

 or glutaminic acid was given, the protein of the mold 

 gave the same cleavage products. There is no doubt, 

 however, that the properties of yeast are greatly influ- 

 enced by the source of nitrogen (p. 238). 



It is imaginable, that certain parasitic forms take 

 large molecular complexes out of their host's native 

 protein, and have lost the power of synthesizing these 

 groups. 



(e) SOURCES OF OXYGEN 



In the discussion of the needs of oxygen for fermenta- 

 tion, the requirements of oxygen for cell growth have 

 been already mentioned for the sake of a more accurate 

 definition of anaerobic and aerobic bacteria (p. 78). 

 It was pointed out there that an analogy exists between 

 the carbon, nitrogen and oxygen requirements, and that 

 the structure of the molecules is probably quite as 

 essential, or eventually more so than the energy relation. 



Carbon, nitrogen and oxygen may be compared in regard to their 

 fitness for growth by arranging them according to the energy required 

 to change them into organic material. 



Carbon Nitrogen Oxygen 



Completely oxidized CO2 HNO3 O3, H2O2 



Partly oxidized CO HNO2 



Molecular C N2 O2 



Partly oxidized | HCOOH NH2CH2CO2H HCOOH 



Partly reduced J 



Completely reduced CH4 NH3 H2O 



