EFFECT OF X-RAYS ON TRIBOLIUM CONFUSUM 



589 



These curves have been dupHcated several times, and although 

 beetles gathered from different brooders at different times give 

 curves of slightly different shape, still all the cm^ves agree very 

 closely with the typical ones shown in figure 4, especially with 

 regard to the 'hump.' 



This would make it seem that at 50 kilovolts, 200 — - — is 



252 



the minimmn lethal dose of X-rays for the least resistant beetles, 



MAM 



and that 500 



252 



is the minimum lethal dose for the most 



resistant beetles. The fact that the 'hump' is always of the 



55^- 



^73- 



'swjy. 



£ii. 



KV 



Fig. 5 Days-life plotted against the logarithm of the X-ray dose at 68 



same form suggests that these beetles which would live 9 days 

 with a dose of 200 ~^^ at 50 KV. would hve a shorter time 



if rayed 250 —^^^ at 50 KV., and that some more slightly 



resistant beetles which would be unaffected by a dose of 200 are 

 killed off at the end of 9 days by a dose of 250. But when a dose 



MAM 

 ^^ ^^^ 2^ ^* ^^ ^^' ^® reached, the most resistant beetles 



are also affected by the rays, so that the whole graph then ap- 

 proximates the probability integral. Further discussion of 

 figure 4 is reserved for a later paper. 



