ABSTRACTS 93 



dish. In this way the agar on both sides of the dish is in perfect con- 

 tact which makes difTusion readily possible. 



These plates are being used to study the effect of spices and condi- 

 ments in inhibiting yeasts, molds, and bacteria. This method serves 

 as a satisfactory means of determining the preserving action of these 

 substances. 



INDUSTRIAL BACTERIOLOGY 

 Under Supervision of D. H. Jones 



A Possible Function of Actinomycetes in soil. H. Joel Conn. 



A comparison has been made at the New York Experiment Station 

 between the number of Actinomycetes in sod and in cultivated soils. 

 The samples have been taken in pairs, one from sod and one from 

 cultivated soil, the two spots selected always being within a few yards 

 of each other. Thirty-five pairs of samples have been taken; and a 

 considerable variety of soil types have been sampled. The compara- 

 tive counts have been made by means of gelatin plate cultures. 



Sod soil, almost invariably, has given a higher count of Actino- 

 mycetes than cultivated soil; also the Actinomycetes have comprised 

 a greater proportion of the total flora in sod soil than in cultivated 

 soil. In the thirty-five samples of cultivated soil, Actinomycetes com- 

 prised, on the average, 20.5 per cent of the total flora; in the samples 

 of sod soil, 37.5 per cent, or almost twice as high a proportion. There 

 were only three or four exceptions in the whole series, and in those the 

 difference in favor of cultivated soil were so small as to be insignificant. 

 The differences in favor of sod soil on the other hand have never been 

 negligible, and sometimes have been extreme — as in one case where 

 Actinomycetes comprised only 2 per cent of the flora in the cultivated 

 sample but 16 per cent in the corresponding sod sample, or in another 

 where they comprised 15 per cent of the flora in the cultivated sample, 

 but actually as much as 60 per cent of the flora in the corresponding 

 sod sample. 



A further series of tests comparing three spots in a single soil type, 

 one fallow, one in new sod, and one in old sod, showed 10-15 per cent 

 Actinomycetes in the fallow spot, 21 to 25 per cent in the new sod 

 and 37 to 39 per cent in old sod. 



The most probable explanation of this difference seems to be that 

 the Actinomycetes are active in the decomposition of grass roots, a 

 point which is now being investigated at the New York Experiment 

 Station. 



Media for Soil Bacteria. H. A. Notes. 



In the course of other investigations in the Horticultural Research 

 Chemistry and Bacteriology Laboratories of the Purdue Agricultural 

 Experiment Station it was necessary to select a medium for the plating 

 of soil organisms. The media first chosen for comparison were the 

 Lipman and Brown agar, H. J. Conn's sodium asparaginate agar, and 

 soil extract agars. Agar-agar alone was also used in comparison with 

 the above media. 



