ENERGY TRANSFORMATION 



393 



lessened (fig. 19). This injury is caused also by other salts in similar 

 osmotic concentrations. A decrease in the concentration of oxygen 

 lessens both growth and respiration, so that at T V atmosphere pressure, 

 respiration is decreased by 66 per cent (fig. 20). This injury is reversible. 

 Growth may be even more injuriously affected than respiration. The 

 optimum and minimum reaction points for respiration lie at pH 5.6 

 and 10.3 respectively, with an optimum pH 8.3 to 9.3 (fig. 17). 17 For 

 growth and respiration definite concentrations of 2 , N0 2 , N0 3 , OH - 

 and traces of H 2 C0 3 are required. The other salts and nutrients 

 play only the part of buffering agents. 



100 



V 



o 



> 



o 



SO 



50 



0,1% 0,5% 



1% 



2% 



3% 



4% 



"Nitrite Concentration 



Fig. 18. Influence of nitrite concentration upon the oxidation velocity of 

 nitrate forming bacteria (from Meyerhof). 



Winogradsky observed the interesting phenomenon that ammonium 

 salts injuriously affect the growth of nitrate bacteria. This seemed 

 rather strange in view of the fact that the nitrate bacteria are active 

 side by side with the nitrite bacteria which use the ammonium salt as 

 a source of energy. It was then' 8 suggested that the two processes 

 follow in two successive periods in the soil, nitrate formation beginning 

 only after all the ammonium salt is converted into nitrite. On de- 



17 As shown elsewhere (p. 528), the limiting and optimum reactions for the 

 growth of the nitrate-forming organism are different from the optima of 

 respiration. 



18 Omclianski, W. tJber die Nitrifikation des organischen Stickstoffes. 

 Centrbl. Bakt. II, 5: 473-490. 1899. 



