SOIL MICROBIOLOGICAL EQUILIBRIUM 



747 



rapidly diminishes. Fischer suggested, therefore, that after a period 

 of decided activities the bacteria become rather inactive although they 

 still show increased numbers; they go into "resting" forms, which 

 possess a low respiratory power, but are capable of developing on the 

 plate into colonies. The rapid increase of bacteria was not found to 

 be accompanied by a similar increase of fungi. The increase in bac- 

 terial activities was considered to be not so much a result of the nu- 

 trients coming into solution during sterilization, but as a result of the 



150 o 



TUB 



Fig. 65. Influence of heating of soil upon the numbers and activities of its 

 population (from Waksman and Starkey). 



decomposition of the bodies of microorganisms in the soil. The in- 

 creased numbers of bacteria bring about an increase in the decomposition 

 of the soil constituents, both of organic and inorganic nature. 



Heating of peat soil, at 100° for fifteen minutes, was found 29 to 

 stimulate greatly the biological activities, when the evolution of carbon 

 dioxide (from 200 grams of soil) was used as an index of these activities. 



29 Demolon, A., and Boischot, P. Sur l'activite" des phenomenes biologiques 

 dans la tourbe. Compt. Rend. Acad. Sci., 177: 282-284. 1923. 



