The susceptibility of cells to radium radiations

Abstract

Among the various factors which influence the response of cells to radium radiations are (1) the temperature of the cells at the time of radiation, and (2) the permeability of the cell membrane. This statement is based on the results of experiments with paramoecium and some other protozoa. The radium, amounting to 13.4 mg of element, was enclosed in a thin-walled glass capsule, and was held at a distance of 2 mm from the water containing the cells. All the paramoecia used were descendants of a single wild cell.

Paramoecium cells are more susceptible to radiations at the upper limit of their physiological range of temperature than at their lower limit. At 14° C. the lethal dose is about 10 hours; at 37° C. it is 1 1/2 hours. These temperatures in themselves are not injurious to the cells. For each rise of 8° C., the length of the lethal dose is halved. In lower temperatures the lethal dose is somewhat shorter than would be expected. The curve expressing these relations is the same as that which expresses the relation between temperature and the rate of metabolism in paramoecium as shown by the rapidity of cell division and of the pulsating of the contractile vacuole.

Cells whose membranes are relatively permeable are more susceptible to radiations than those whose membranes are relatively impermeable. The permeability of paramoecium and other protozoa is determined by the rate at which dilute NH₄OH enters the cells and decolorizes the neutral red in which they have been stained. At different periods of its life cycle, paramoecium shows varying permeability. During conjugation the cells destain in 7 minutes, when treated with n/1500 NH₄OH, while single cells destain in 20 minutes.