PROLONGATION OF LIFE DUE TO X-RAYS 



453 



TABLE 3 



Table 3 gives tfie death rate per 100 in each group for A, B 

 and C. 



It is evident that the smallest daily dose (group IW) decreases 

 the death rate of 'A' and that those beetles which are kept from 

 dying of 'A', die of 'B.' Deaths from cause 'C are practically 

 unaltered. A larger daily dose (group IX) causes about half of 

 those which would normally die of 'A' to die of 'C A still 

 larger daily dose (group lY) causes half of those which would 

 have died of 'A' to die of 'B' and 'C A still larger daily dose 

 (group IZ) acts much like the previous dose in causing almost 

 half of those which would have died of 'A' to die of 'B,' but it 

 differs from it in that some of those which would have died of 

 'C are prematurely killed. The largest daily dose employed 

 (group JA) caused about a third of those which would have died 

 of 'B' and 'C to die of 'A.' 



It is hard to interpret all this. It may be that life cannot 

 exist except in the presence of a small amount of radio-activity. 

 The radio-activity of the earth may not have been of the 

 optimum value, so that some benefit was derived from the x-rays 

 received each day. The following is an effort at an alternative 

 explanation. The evidence given by group JA shows that the 

 lethal action of x-rays is tied up in some way with cause of 

 death 'A.' It is well known that the lethal action of x-rays is 

 more marked on cells in the process of division than on those in 

 the resting state. Therefore, small daily doses (larger than a 

 certain minimal value) can kill off those few cells which happen 

 to be in a state of division at the time of raying. The death of 



