582 



WHEELER P. DAVEY 



little cornmeal, and was kept closed during the raying. The 

 X-rays, therefore, after leaving the X-ray tube, passed through 

 0.025 nun. of Al and 3 mm. of wood before reaching the beetles 

 and cornmeal. At the voltage employed in this work to date 

 (50 KVjjjjg), the error due to absorption of X-rays by the small 

 thickness of Al and wood was very small. 



EXPERIMENTAL 



Two or three thousand beetles were gathered from the same 

 brooder on the same day and put into a large granite-ware pail. 

 The next morning they were packed with a little sterile cornmeal 

 in the wooden boxes mentioned above, — 25 in each box. In this 

 way the distribution of age, susceptibility to X-rays, etc., was 

 as nearly uniform as possible. From this time on the tightly 

 closed boxes were kept in incubators at 35° to 36°C. and at sat- 

 urated humidity, except while being X-rayed or while being 

 counted. Every box was opened daily, the beetles separated 

 from the cornmeal and a record made of the number of live and 

 dead beetles. The assistants who did this counting had no 

 way of knowing the dose of X-rays which had been given. 



After all the beetles in a given group of boxes were dead, the 

 data sheets were collected and the data combined as shown in 

 table 1. From 4 to 8 control boxes were used with each ex- 

 periment to make sure that the beetles were in every way nor- 

 mal. The normal death rate at the end of the first 15 days was 



TABLE 1 



MAM 

 Beetles rayed 2000 at 50 KV 



