Abstract
(1) The addition of amino-acids to a medium resulted in the protection of E. coli irradiated with cobalt-60 gamma-ray.
(2) The tendencies of the protective effects differed from each other. From this viewpoint, they could further be divided into four groups.
(3) In order to compare the protective effect of each amino-acid, the Sin-value obtained from each survival-curve was chosen as the indicator.
(4) Proline was found to be most protective, and phenylalanine the least, whereas arginine was not protective.
(5) The addition of proteinous materials also resulted in the protection of E. coli irradiated with cobalt-60 gamma-ray.
(6) The addition of proteinous materials to nutrient agar medium resulted in only weak protection. However, their addition to a minimum medium was very protective.
