324 



RECOVERY FROM FLUORITE RAYS 



had usually undergone fission. From previous experiments^ on the 

 effects of these rays on Paramecium caiidatum we have learned that 

 if the organisms are actively swimming 24 hours after the radiation, 

 they will continue to live and will multiply at the same rate as the 

 non-radiated controls. The experimental results are given in Table I. 

 It will be seen from Table I that as the interval of time between 

 the two exposures increases, the per cent of cytolized organisms de- 

 creases. During the time between the two exposures the organism 

 recovers from the effects of the first 4 second exposure so that when 

 the second 4 second exposure is added the total effect is less than 

 that of a single 8 second exposure. The amount of this recovery in- 



TABLE I, 



Rate of Recovery from the Action of Fluor He Rays. 



After one exposure of 4 seconds the per cent of cytolysis was 7. 



creases as the interval of time between the two exposures increases. 

 For example, when the interval of time between the two exposures 

 was 1 hour, the organism had so completely recovered from the effect 

 of the first exposure that the combined effect of the two exposures 

 was no greater than that of a single 4 second exposure. 



7 per cent of all the organisms receiving a single 4 second exposure 

 cytolized. If we subtract 7 per cent from each of the percentages 

 given in Column 4 of Table I, we obtain the values given in Column 

 5. These values are plotted in Fig. 1 as ordinates against the inter- 

 vals of time as abscissas. The points fall upon a smooth curve. The 

 shape of the curve suggested that the process of recovery might be 

 adequately represented by the equations which govern homogeneous 



