454 WHEELEE P. DAVEY 



these few cells stimulates the production of more to take their 

 places between the periods of raying. Therefore, small daily 

 doses, instead of increasing the death rate from cause 'A,' 

 actually decrease it by stimulating the processes of repair. The 

 whole individual beetle, therefore, has a smaller chance of dy- 

 ing from 'A' and is compelled to die of either 'B' or 'C When 

 the daily dose is increased to such a value that the daily de- 

 struction of cells is equal to or greater than the production of 

 new cells, premature death occurs, from causes 'B' or 'A' (see 

 groups IZ and JA). 



B. PROLONGATION OF LIFE DUE TO SMALL SINGLE DOSES OF 



X-RAYS 



Five groups of approximately 850 individuals each were 

 taken. These were known as groups JB, JC, JD, JE and JF. 

 Group JB was the control. 



Group JC was given 100 ^^^ at 50 KV. - 50 M.A. 



MAM 

 Group JD was given 200 ;- at 50 KV. - 50 M.A. 



MAM 

 Group JE was given 300 ~ at 50 KV. - 50 M.A. 



MAM 

 Group JF was given 400 -^^ at 50 KV. - 50 M.A. 



The beetles were rather old, so that the controls were all dead 

 on the fortieth day of the experiment. There were so few bee- 

 tles still alive after the thirty-fifth day that the results of the 

 last five days are not of the same order of accuracy as those of 

 the first thirty-five days. 



MAM 



The first ten days of the experiment, group JC (100 



25^ 



at 50 KV.) had the same death rate as the controls. After the 

 tenth day the death rate was considerably less than that of the 

 controls. The two groups were divided into two equal sub- 

 groups, and although it was found that the idiosyncrasy was 

 such that the subgroups were not exactly ahke, still, after the 



