392 



PRINCIPLES OF SOIL MICROBIOLOGY 



normal and the carbon was derived from the NaHC0 3 in the medium. 

 In the presence of CO2 in the atmosphere, the bicarbonate was found to 

 serve as a buffering agent in the medium keeping the reaction at 

 pH 8.8 which is optimum for the activities of these bacteria. When 

 phosphates were used as buffering agents the organism was found to 

 make a normal growth, using the C0 2 coming into solution from the 

 atmosphere. No growth took place in the total absence of C0 2 . 



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1 



c 



o 



■9 

 o 



» -f>m __, ^ 



» f- _ jLo 



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ol — I — I — I — L_J — I — I — I — I — EL 



;.i 1.8 7.8 8.0 



Fig. 17. Influence of reaction upon the respiration of nitrite-forming bacteria 

 (after Meyerhof). 



For the study of respiration, Meyerhof grew the organism in the 

 general medium till a good growth had taken place. A certain con- 

 centration of the nitrite was introduced into a definite volume of cul- 

 ture and the flask placed in thermostat. The change produced in a 

 definite period of time (usually 4 to 6 hours) was taken as a measure 

 of the respiratory power of the culture. Meyerhof demonstrated that, 

 outside of the nitrite oxidation and carbon assimilation, no other reac- 

 tion takes place in the process of energy transformation. The nitrate 

 organism utilizes only the nitrite-ion as a source of energy and no other 

 substance. 



With an increasing nitrate content, growth and respiration are 



