STUDIES ON THE DURATION OF LIFE 221 



life to a degree which, in the case of the males, may be 

 regarded as probably significant statistically. In the 

 case of the females, where the ratio of the deviation to 

 its probable error (Dev. /P. E.) falls to 2.25 the case 

 is very doubtful. The procedure by which the chance of 

 1 :150.2 that results in both sexes together were acciden- 

 tal, was obtained is of doubtful validity. Putting males 

 and females together from the original table, I find the 

 following results. 



TABLE 28 



Duration of life of white mice, both sexes taken together 



(From data of Robertson and Ray) 



One concludes from these figures that tethelin can be 

 regarded as having lengthened the span of life to a de- 

 gree which is just significant statistically. One would 

 expect, from the variation of random sampling alone, to 

 get as divergent results as these about 1% times in every 

 100 trials with samples of 64 and 39, respectively. 



In any event it is apparent that, making out the best 

 case possible, the differences in average duration of life 



