SummaryA loam soil of pH 8.0, supplemented with 1 of glucose, was irradiated with gamma rays at doses from 0.1 to 1 Mrad. Microbial counts were made immediately after irradiation, and after 15 and 30 days of incubation. The higher the dose, the greater the damage to micro‐organisms, but even the highest dose did not completely sterilize the soil. Azotobacters were killed by 1 Mrad and very much reduced in numbers by smaller doses. Clostridial spores were unaffected by 0.1 Mrad, and more resistant than azotobacters to larger doses. Streptomycetes developing on agar plates were more affected than bacteria at first, but during incubation the number of streptomycetes in the irradiated samples increased to more than the number in nonirradiated controls. Doses of irradiation that are too small to sterilize a soil evidently upset the equilibrium between bacteria and streptomycete
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