SUMMARY: The number of micro-organisms present in soil located at a distance of 4 cm. from a 60Co-source 1 m. above ground declined considerably after 24 hr. of exposure. Respirometric determination showed no decrease in oxygen uptake at this time. The distance at which the effect of irradiation could be demonstrated increased with increasing duration of exposure; after 396 days a reduction of the oxygen uptake as well as of the number of microbes could be detected at a distance of more than 3 m. and at a depth of 10 cm. as well as at the surface.
There appeared to be no significant difference between the effects of chronic irradiation on spore-forming and on non-spore-forming bacteria, respectively.
The plot of microbial count showed a better fit to a double-logarithmic than to a semi-logarithmic diagram according to Lea’s formula. Possible explanations of this fact are discussed.
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