450 WHEELER P. DAVEY 



These readings, taken from the smooth curves of the graphs, 

 do not differ from the actual experimental data by more than 1 

 per cent. 



Except while being x-rayed or counted, the beetles were kept 

 in an incubator at 34 to 35°C. In order to make sure that the 

 results were not affected by some possible 'temperature co- 

 efficient of life,'^ the controls were taken out of the incubator 

 while group JA was being rayed, and were kept out during the 

 whole raying. Since group JA was rayed the longest time each 

 day, this meant that the controls were cooled off for a longer 

 time than groups IW, IX, lY, IZ. Therefore, if cooling off for a 

 few minutes each day happened to tend to increase the length 

 of life, then the controls were made to live longer than they 

 otherwise would. The actual increase in length of life observed 

 in groups IW, IX, and lY is, therefore, not due to any possible 

 effect of temperature, but occurs in spite of it. After so many 

 boxes of beetles in JA were dead that the time of raying group 

 IZ was greater than the time of raying JA, the controls were 

 kept out of the incubator while group IZ was being rayed. 



Some data not given in the graphs may be of additional in- 

 terest. Each group was divided into two subgroups of about 

 the same number of individuals each. It was found that the 

 idiosyncrasy was great enough so that the curves of the corre- 

 sponding subgroups could not be exactly superimposed. How- 

 ever, it was found that this idiosyncrasy was always less than 

 the changes in death rate caused by x-rays. By way of illustra- 

 tion, table 2 shows the percentage of beetles dead in each sub- 

 group, a) on the day when 50 per cent of the controls were dead; 

 (6) on the day when 50 per cent of the x-rayed group were dead. 

 This table shows that the lowest death rate among the controls 

 (group IV) was higher than the highest death rate among the 

 beetles of groups IW, IX, lY. 



It is interesting to note in this connection that the total dose 

 received by these beetles was greatly in excess of that minimum 

 dose which, when given all at once, would have caused pre- 

 mature death. 



» Loeb and Northrup, Proc. Nat. Acad. Sci., Aug., 1916. 



