THE EFFECT OF X-RAYS ON BACTERIA.
(1) X-rays act like sterilizing agents upon cultures of B.coli and Erythrobacillus prodigiosus, in that the curves are characteristic sterilization or death-rate curves showing that the total counts decrease logarithmically with time. (2) In this experiment B.coli did not show variation or mutation when it was treated with X-rays. (3) With increasing irradiation Erythrobacillus prodigiosus showed a tendency toward lack of ability to produce its characteristic red pigment. By allowing the organism to grow on the plate for a period of five days the greater portion of the colonies produced their pigment. If a transfer of a white colony is made to an agar slant the characteristic pigment is produced in twelve hours. In only one case was it necessary to make a second transfer in order to bring about the development of the pigment. The above is another example of the variation tendency of Erythrobacillus prodigiosus.
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