No. 646] 



THE DURATION OF LIFE 



397 



periment give no suggestion that with larger dosage any 

 such result would appear, and in the second place, be- 

 cause the experiments of Bacot and Harden (48) indi- 

 cate that as slight (or slighter) alterations of the food 

 of Drosophila as those of the present experiments may 

 produce marked effects in respect of viability.^ 



For some reason which we are unable to explain, the 

 flies of Line 107 had, in all the series of this experiment, 

 a lower mean duration of life than this line has ever 

 shown before (c/. 32, 44, and section A of the present 

 paper). The values are extremely even and consistent 

 in this feeding experiment, but are about 10 days lower 

 than what previous work has indicated as the normal 

 duration of life in this line. There has been no other 

 change in the line, in fertility or other characters. We 

 are inclined to believe that the low values in the present 

 experiments represent merely a temporary secular 

 change ( ? seasonal) in the duration of life characteristic 

 of the line. 



Summary 



In experiments involving the determination of the 

 duration of life in 2,990 individual flies, it was found that 

 there was no prolongation of the life of Drosophila pro- 

 duced by adding embryonic juice (either from the chick, 

 or from the larvae of Drosophila itself) daily to the food, 

 to the amount of 2 per cent, of the total food material, 

 beginning with the 31st day of the flies' life. 



LITERATURE CITED 

 (The plan of numbering citations is explained in the second of these 

 Studies, Amer. Nat., Vol. 56, p. 174.) 



44. Pearl, R. and Parker, S. L. Experimental Studies on the Duration of 



Life. III. The Effect of Successive Etherizations on the Durfrtion of 

 Life of Drosophila. Amer. Nat., Vol. 56, pp. 273-280, 1922. 



45. Frisch, A. and Starlinger^ W, Zur Frage der ProtopIasma-a<:tivierung. 



ZeitscJir. f. d. ges. exp. Med., Bd. 24, pp. 142-158, 1921. 

 3 It ought, however, to be pointed out that the experiments of Bacot and 

 Harden are extremely faulty from a technical standpoint. They evidently 

 know little of the practical husbandry of Drosophila. Their cultures were 

 incubated at 30° C. At this temperature one does not get anything remotely 



