No. 646] TEE DURATION OF LIFE 393 



be hoped for. In view of the known facts as to the po- 

 tential immortality of tissue cells in cultures in vitro, and 

 the apparent reason for the difference in the behavior of 

 the same cells in respect of duration of life when they are 

 in the multicellular body, all of which has been rather 

 fully discussed by Pearl in the "Biology of Death" {loc. 

 cit.), it would seem that this is a line of experimenta- 

 tion well worth following. We have a number of experi- 

 ments along this line now in progress, particularly with 

 X-rays, which we expect later to report upon. Some of 

 the purely preliminary work has already been finished, 

 and we wish in this paper to report one piece of it. 



The brilliant researches of Carrel and his coworker 

 Ebeling {cf. 46, 47) on the duration of life of cells in 

 cultures in vitro have brought to light the extraordi- 

 narily interesting and presumably important fact that 

 for the continued life of such cultures it is apparently 

 essential to have in the culture medium a small amount 

 of embryonic juice. In just what manner this functions 

 is not yet clear, but the necessity of its presence seems 

 well established. 



It occurred to us in our preliminary work on prolonga- 

 tion of life in Drosophila, or as it is perhaps better to 

 put it, on changing the form of the L line of the Droso- 

 phila life table, to see whether embryonic juice, applied 

 at a point on the L curve after senescence had definitely 

 set in, would have any effect upon the subsequent course 

 of the curve, or in otber words, upon the duration of life 

 of the organism as a whole, comparable to its effect upon 

 the life of cells in culture. The ideal way, of course, in 

 such an experiment would be to get the embryonic juice 

 to the tissues of the fly by a par-enteral route, but as no 

 practical method of doing this occurred to us, we decided 

 to feed it, and see if any results followed. 



Material and Methods 

 The flies used in the experiment were all wild type, of 

 Old Falmouth stock, and belonged to Line 107, pedigree 



