89 



tolerance of soil mlcro organisms to media 



Changes. 



H. A. Notes. 



Our text books all give space to the discussion of the food requirements 

 of bacteria. The discussion, although general, is liable to lead us to believe 

 that most orgamsms may not grow if we change the composition of media 

 slightly. Just what is the minimum ration for most bacteria is not known. 

 Our knowledge of the effects of modifying the composition of culture media 

 is meager, especially when environmental factors are considered. 



The Horticultural Research Chemistry and Bacteriology Laboratories, 

 of the Purdue Agricultural Experiment Station have been investigating 

 media for the platings and subsequent culturing of soil bacteria. This paper 

 reports a part of this investigation. 



Soil Used. 



Two types of soil were used in this work, silty clay from the Experimental 

 orchard at Laurel. Indiana, and brown loam from the Station orchard where 

 a cover crop investigation is under way. All samples reported on in this paper 

 contained from 16 to 20 per cent, of moisture at time of sampling. The 

 method of sampling was by means of Xoyes' sampler for soil bacteriologists. 

 Samples were taken of the upper nine inches of soil. 



Media Used. 



Lipman and Brown "synthetic" agar. 

 15 gms. best agar. 

 10 gms. Dextrose. 

 .05 gms. Witte Peptone. 

 . 2 gms. Magnesium sulphate. 

 .5 gms. Di potassium hydrogen phosphate. 

 Trace Ferrous sulphate. 

 1,000 cc. Distilled water. 



H. J. Conn's sodium asparaginate agar. 

 15 gms. best agar (used instead of 12). 



