Sensitization to Heat by X-Rays

Abstract

1. Paramecium caudatum is sensitized to heat by sublethal dosages of x-rays. Thus if paramecia are irradiated, then exposed to a sublethal dosage of heat they are killed, but if the same heat exposure precedes the same dosage of radiations, they are not. 2. Sensitivity to both heat and x-rays is much greater in paramecia from the log growth phase than in those from the stationary phase of a culture. 3. Recovery from heat sensitization in animals from the stationary phase of a culture is slow, requiring several days. 4. Division is readily retarded and even temporarily inhibited by sublethal dosage of x-rays. Recovery of the division rate is fairly slow requiring several days. 5. Paramecia can be killed by a dosage of 1,200,000 r (of which about one-half reach the animal) units of x-radiation alone. Smaller dosages are not lethal if the paramecia are transferred to fresh medium immediately upon completion of irradiation. 6. The possibility of utilization of heat sensitization in treatment of malignant growths is discussed.

The Effect of X Radiation on the Respiration of Escherichia Coli

“…The observation that the total activity of the oxidative system in exposed cels is greater within a given time at 26 C than at 37 C is suggestive of the existence of an abnormally heat-sensitive respiratory system in these cells. Giese and Heath (1948) reported that sublethal dosage of soft X rays increased the sensitivity of Paramecium caudatum to heat. We have observed also that cells held in phosphate buffer after irradiation show a marked drop in number of viable cells if the incubating temperature is 37 C as compared to a less pronounced decrease at a temperature of 25 C and below (unpublished data of the authors).…”