226 



Scientific Proceedings (128) 



109 (2069) 



The susceptibility of cells to radium radiations. 

 By CHARLES PACKARD. 



[From the Peking Union Medical College, Peking, China.] 



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 para- 

 moecium 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. ! \ m \ 



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 \ l /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 express- 

 ing these relations is the same as that which expresses the rela- 

 tion between temperature and the rate of metabolism in paramoe- 

 cium as shown by the rapidity of cell division and of the pulsating 

 of the contractile vacuole. 



Cells whose membranes are relatively permeable are more sus- 

 ceptible to radiations than those whose membranes are relatively 

 impermeable. The permeability of paramoecium and other 

 protozoa is determined by the rate at which dilute NH^OH 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 w/1500 NH 4 OH, while single cells 

 destain in 20 minutes. At 21° C. the lethal dose of radiation for 

 conjugating cells is 3 l / 2 hours: that of single cells is 5j4 hours. 

 A comparison of the permeability of paramoecium with that of 

 Stylonichia shows that the former cells destain in about one- 



