EFFECT OF X-RAYS ON TRIBOLIUM CONFUSUM 



585 



■LOG POSE 



Figure 2 B 



Fig. 2 A, curves showing percentage of beetles dying each day after raying' 

 B, days-life plotted against the logarithm of the X-ray dose. 



This gives a method of handhng the data which not only ehmi- 

 nated errors due to idiosyncrasy, but which even gives a measure 

 of idiosyncrasy which is accurate enough between the limits of 

 '25 per cent dead' and 75 per cent dead. Figure 2 A shows a 

 series of results obtained in this way in which even the 10 per 

 cent and 90 per cent points could be used. Before discussing 

 figure 2 B, it will be necessary to explain the methods of re- 

 cording X-ray dosage. 



In order to define the quantity of X-rays and the bundle of 

 wave-lengths used in a given experiment, it is necessary to record 

 explicitly 



1) the material used as a target in the X-ray tube. 



2) the thickness and kind of filters (if any). 



3) the form of the voltage wave. 



4) the form of the current wave. 



The following must be recorded either explicitly or implicitly: 



5) voltage across the X-ray tube. 



6) current through the tube. 



7) the length of time the X-rays were employed. 



8) The distance from the focal spot of the X-ray tube to the 

 point to be rayed. 



If 1, 2, 3, 4 are kept constant throughout the experiment, 

 they may be stated once for all (as was done in this report under 

 the head of 'apparatus'), and the dose of X-rays may then be 

 defined by either of two methods: 



a) The voltage may be expressed directly, or an approxi- 

 mation may be given in terms of the readings of a Benoist pene- 



