W. T. BOVIE AND ALICE KLEIN 335 



Total No. of organisms radiated 20 



No. of deaths 4 



Per cent of death 20 



Experiment 7 . Recovery Period 1 Hour. — Organisms were radiated 

 for 4 seconds at 17-18°C., and after 1 hour at 17-18°C. were exposed 

 on a temperature slide to 24-28°C. for 60 seconds. 



Total No. of organisms radiated 21 



No. of deaths 1 



Per cent of death 5 



Experiment 8. Recovery Period 5 Hours. — Organisms were radi- 

 ated for 4 seconds at 17-18°C., and after 5 hours at 17-18°C. were 

 exposed on a temperature sUde to 24-28°C. for 60 seconds. 



Total No. of organisms radiated 24 



No. of deaths ; 



Per cent of death 



The organisms had nearly recovered from the heat sensitization 

 caused by the exposure to fiuorite rays in 1 hour, and had completely 

 recovered in 5 hours. In this ability to recover the heat-sensitized 

 Paramecium differs from the heat-sensitized egg white, since the 

 latter does not recover however long the interval of time between 

 the radiation and the exposure to heat. 



The results of these experiments are clear cut, and show that 

 Paramecia which have been exposed to fiuorite radiation are so sen- 

 sitized to heat that they are unable to withstand, even for 60 seconds, 

 temperatures which are optimum for non-radiated controls. 



Woodruff and Baitsell^ found normal Paramecia from a pedigreed 

 culture able to withstand a temperature of 32° for about 2 days. 



In the experiments on egg white, referred to above, it was shown 

 that egg white which is maintained at 0°C., during the exposure to 

 ultra-violet light, will, with the proper amount of exposure, coagu- 

 late when it is warmed to room temperature. On the other hand, 

 egg white which is maintained at room temperature while receiving 

 an equal amount of exposure coagulates during the radiation. Now 

 in this case it might not be improper to say that the coagulation is 

 in reality not photocoagulation but is heat coagulation. The egg 

 white has been heat sensitized by the radiation so that it can no 



