THE SUSCEPTIBILITY OF CELLS TO RADIUM RA- 

 DIATIONS. 



CHARLES PACKARD. 



PEKING UNION MEDICAL COLLEGE. 

 DEPARTMENT OF BIOLOGY. 



1 t has frequently been observed that cells may show at different 

 periods of their existence marked variations in susceptibility to 

 radium radiations. An embryonic cell is more quickly injured 

 than the same cell in the adult condition: at the metaphase, 

 cells are more sensitive than they are immediately before or 

 after that brief period (i). Bohn (2) first suggested that the un- 

 derlying cause of such differences in response must be sought in the 

 physiological condition of the cells at the time of radiation. That 

 they cannot be due to changes in the absorptive power of proto- 

 plasm is obvious: whether a cell is sensitive or not, the rays are 

 absorbed to the same extent. The actual changes produced by 

 them in protoplasm must therefore be the same. But the reac- 

 tion of the cell to such changes differs immensely. \\e may 

 therefore say that a cell is susceptible when it is in such a physio- 

 logical condition that a modification produced by the rays re- 

 sults in a greater or less injury, and that it is resistant when the 

 same modification is not followed by injurious effects. 



The object of the present paper is to show that among the con- 

 ditions which affect the susceptibility of cells to radium nidia- 

 tions are (i) the temperature of the cells at the time of exposure, 

 and (2) the relative permeability of the surface layer of the cell. 



The experiments to be described were carried out on certain 

 Protozoa, for these cells are better adapted to this kind of experi- 

 mentation than any others. They can live in both high .md low 

 temperatures without injury: and different genera show in. irked 

 differences in permeability. Cells of the same species, even 

 descendants of the same individual, vary widely in their re.ictic.n 

 to radium radiations at different periods of their life cycle, 

 is perhaps the best cell for experimental purposes 

 it is more susceptible than any other common type. 



