THE 



AMERICAN NATURALIST 



Vol. LVI. Septe he October, 1922 No. 646 



EXPEEIMENTAL STUDIES ON THE DURATION 

 OF LIFE 



V. On the Influence of Certain Environmental 

 Factors on Duration of Life in Drosophila^ 



PEOFESSOE EAYMOND PEAEL AND SYLVIA L. PAEKER 



A. Influence of Ventilation on Duration of Life 

 The standard method of handling Drosophila cultures, 

 as described by Pearl and Parker (27), includes the 

 plugging of the mouth of the bottle with absorbent 

 cotton to prevent the escape of the flies. The theory of 

 this practice, which is the custom in Morgan's labora- 

 tory, presumably is that air will pass in and out through 

 the plug while the flies can not. No physicist or ventila- 

 tion engineer w^ould, we believe, accept this theory. 

 Many years ago the senior author had occasion to make 

 some observations on the ventilation of curtain-front 

 poultry houses, and soon came to the conclusion that 

 curtains of one thickness only, of the very porous jute 

 bagging which is used for bran sacks, are practically 

 nearly as effective in preventing the natural unforced 

 circulation of air as a half-inch pine board would be. 

 We may be sure that the plug of cotton used in Droso- 

 phila bottles will be an even more certain preventative 

 of the natural unforced circulation of air. Theoretically 

 one may perhaps hold that there is more circulation of 

 air with a cotton plug than there would be with a cork 

 stopper, but the difference must be infinitesimal. 



1 Papers from the Department of Biometry and Vital Statistics, School of 

 Hygiene and Public Health, Johns Hopkins University, No. 67. 



385 



