Abstract
1) Despite the bacterial concentration, the survival-curves of E. coli are approximately constant at the highest concentration of 107 cell/ml and at the lowest, 102 cell/ml.
2) In this case, the mass of points covers a wider range as the bacterial concentration is raised.
3) In this method, since the radiation time is shorter and there is less probability of appearance of mutants, the medium containing a concentration of 102 cell/ml seems to be most satisfactory.
4) A comparison of gamma-ray resistivity of each type of bacteria, using a medium of 102 cell/ml concentration has been made.
5) Moreover, the influence of chemical substances upon the lethal effect of gammaray on E. coli was investigated.
Acknoledgements. The author wishes to exprss his cordial thanks to Prof. T. Obara, Dept. of Agricultural Chemistry, Tokyo Univ. of Education, for his direction and generous guidance. He is also indebted to Prof. D. Ushiba, Asist. Prof. S. Sasaki, Dept. of Bacteriology, Keio Univesity, for their guidance, and to Prof. T. Asai, Dr. M. Amaha, Dept. of Agricultural Chemistry, Univ. of Tokyo, for their helpful and kind advice. Thanks are also due to Asist. Prof. H. Yamashita, Dept. of Radiology, Keio University, for his sound advice concerning radio-isotopes.
