SUSCEPTIBILITY OF CELLS TO RADIUM RADIATIONS. i;i 



staining time varied from 7.8 minutes to 9 minutes. In a culture 

 which was undergoing an epidemic of conjugation the pairs 

 showed an average destaining time of 4.5 minutes. This culture 

 was presumably not pure, and the pairs in their reaction to the 

 ammonia showed a wider variation than was found in any homo- 

 geneous group. But the difference in permeability between con- 

 jugant- and non-con jugants was in every case large enough to be 

 !iiti .nit. 



Other Protr>/na diitcr from Paramcecinm in permeability. A- 

 Har\ey ha- puinted out, Stylonichia and Oxytricha are compara- 

 ti\elv impermeable. Indeed, after ten minutes in neutral red 

 : ie ii-u il <Min duration they have taken up almo-t no color at 

 all. The -lain must act for twenty-five to thirty-five minutes 

 IK hui ilic- <-i-lls are stained sufficiently for experimental pur- 

 poses, and e\en after this time they are not as hiyjily coloiv: 



iniii'innt \> after ten minutes. The time required fur <K- 

 stainini; Stylonichia varies somewhat in different cultures, but 

 tin- average is approximately forty minutes. 



\\ hen the relative permeability of these cells is compared with 

 the length of their lethal dose of radium radiation-, we find a 

 di.-e tuMvlation between the two measurement-: that i-. cells 

 \\hich are relatively permeable are quickly killed by the i 

 \\hile those which are less so are more resistant. The following 

 table indicates these relations. 



< "MI'AKISON OF THE DESTAINING TlME AND LETHAL I> R\D|iM R \IHA- 



TIOSS AT 27 C. 



Destaining Time. Lethal I' 



/'.; am ' >>n single cells 8.6 min. i \\ 



: KUijiiK.itintJ 4.5 min. i ' _, li< 



nia 40. min. 15!. 



It is evident therefore that the susceptibility of thc-e 1 Y. itozoa 

 to radium radiations varies directly with the permeability of the 

 surface layer of the cell. 



Tin-: EFFECT OF RADIUM RADIATION- ON mi-: CELL MKMHR\NE. 

 The question naturalU arises, what is the reason for this corre- 

 lation? The an-\\er is to be found in the fact that the rays which 

 are absorbed produce in the cell membrane changes which lead 

 to increased permeability. The experiments described below 

 indicate the rate at which these changes take place. 



