396 THE AMERICAN NATURALIST [Vol. LVI 



It is evident that there are no large differences in 

 mean duration of life between any of the groups. The 

 Ix distributions and the constants are closely similar 

 throughout. This is true whether the whole life is taken, 

 or the expectation after age 31. The exact nature of the 

 differences is shown in Table VII. 



TABLE VII 

 Differences in Means op Table VI 



The control group had slightly the greatest duration 

 of life, both as a whole, and from the time of the begin- 

 ning of the special feeding on. The flies fed larval pulp 

 had the worst expectation of life, with those fed chicken 

 juice in an intermediate position. None of the differ- 

 ences, however, is large. That some of them are signifi- 

 cant statistically probably means no more than that the 

 changed food is not quite so favorable for the flies as the 

 normal, standard food. The numbers involved are large 

 relatively, and the probable errors consequently small. 



We must then conclude that the administration of em- 

 bryonic juice in the manner, amount and time in the life 

 cycle, which defined its administration in these experi- 

 ments, does not bring about any prolongation of the life 

 of the whole organism, comparable to its effect in tissue 

 cultures in vitro. This does not necessarily mean that 

 under other conditions of administration or dosage an 

 effect in this sense might not be produced. We believe, 

 however, that it is not probable that any prolongation 

 of life can be brought about by this method, for the rea- 

 son that in the first place the results of the present ex- 



