EFFECT OF X-RAYS ON TRIBOLIUM CONFUSUM 591 



ess of repair went on inside the beetle, and if there were no 



other cause of death present. 



It will be noticed that this formula takes no account of any 



cause of death other than X-rays, nor of any process of repair 



which may go on inside the beetle. It therefore applies only 



when the X-ray dose has been large enough to completely destroy 



the protective mechanism of the beetle, and when the damage 



caused by the X-rays is large enough so that all other causes of 



death may be neglected. The minimum dose for which this is 



■ MAM 

 true is 500 ^^4^ at 50 KV. 

 252 



It should be noted that length of life after raying is a meas- 

 ure of the resistance of an organism to X-rays, not of its sus- 

 ceptibility. If X-rays are able to kill the organism in two dif- 

 ferent ways, as by attacking two different kinds of cells, or two 

 different organs, then the experimental graph should be the re- 

 sultant of two straight lines, but in such a case it must be re- 

 membered that susceptibilities not resistances are to be added. 



The graphs shown above seem to indicate that Tribolium con- 

 fusum are affected in two ways by the X-rays, the threshold 



MAM 



dose being, for the first way, 500 ^ at 50 KV., and for the 



second way about 4000 J at 50 KV. These graphs would 



also seem to indicate that the cause of death for dosages between 



500 and 4000 is negligible in the presence of that for dosages 



MAM 



above 4000 ^^^ at 50 KV. 



z5^ 



SUMMARY 



1. It has been shown that the lethal effect noticed on Tribo- 

 lium confusum beetles after X-raying is really due to X-rays 

 and not to some accidental circmnstance. 



2. A method has been developed which eliminates the error due 

 to idiosyncrasy, thus making it possible to obtain bio-physical 

 data of a considerable degree of precision. 



