89 
TOLERANCE OF Sort Micro OrGANIsmMs To MEDIA 
CHANGES. 
Hey Ac UNoxyEs: 
Our text books all give space to the discussion of the food requirements 
of bacteria. The discussion, although general, is Hable to lead us to believe 
that most organisms 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. 
Soin UseEp. 
Two types of soil were used in this work, silty clay from the Experimental 
orehard 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 Noyes’ sampler for soil bacteriologists. 
Samples were taken of the upper nine inches of soil. 
Mepra USeEp. 
‘ 
Lipman and Brown “‘synthetie”’ agar. 
15 ems. best agar. 
10 gms. Dextrose. 
.05 gms. Witte Peptone. 
.2 gms. Magnesium sulphate. 
.9 gms. Di potassium hydrogen phosphate. 
Trace Ferrous sulphate. 
1,000 ce. Distilled water. 
H. J. Conn’s sodium asparaginate agar. 
15 gms. best agar (used instead of 12). 
