274 THE AMERICAN NATURALIST [Vol. LVI 



ation. In Drosophila these two factors can be separated. 



It has seemed important, in an early stage of our ex- 

 perimental work on the duration of life in this form, to 

 make a careful and extensive experimental test of the 

 question of whether anesthetization singly or repeated 

 changed in any way the expectation of life or form of 

 the life curve, so that if this factor does have any sig- 

 nificant influence, either favorable or unfavorable, due 

 allowance may be made for it. It is the purpose of this 

 paper to report the results of such a test. 



The flies used in this experiment were flies of line 107 

 (generation 8 since January 14, 1921, line bred from a 

 single brother and sister mating for approximately 30 

 generations). The characteristics of this line relative to 

 duration of life have already been described {cf. Pearl 

 and Parker (32)). The 4,330 flies used emerged between 

 10 A.M. April 18, 1921, and 4 p.m. April 22, 1921, from 

 thirty-five mass cultures started in half-pint milk bottles 

 April 7, 1921. The regular procedure in these experi- 

 ments was to collect the flies from all 35 breeding bottles 

 in one empty bottle and then to count the flies through 

 a counting tube into 1-ounce vials, allowing 50 flies to 

 each vial.^ Ten vials were used for each series, except 

 the control series, which had 18. For two of the series 

 only two hours were allowed between successive empty- 

 ings of the mating bottles, to get flies at an average age 

 of one hour, assuming that they emerged uniformly over 

 the interval. One series was etherized as soon as counted 

 out, and the other series kept as a special control group 

 to see if the handling when the flies were so young and 

 soft had any effect on the duration of life. For the rest 

 of the series the flies were allowed to emerge over a 24- 

 hour interval. Each day's hatch was divided randomly 

 and as equally as possible among the different series. 



