A STUDY OF OXYGEN METABOLISM. 457 



It is believed that under the conditions of the experiment 

 food conditions were maintained as nearly uniform as is possible. 

 Moulds occasionally became established in the culture vials but 

 the growth rarely if ever became noticeable until after the larvae 

 had pupated. It is altogether possible that organisms harmful 

 to the larvae and of sporadic occurrence in the tubes may have 

 contributed in slight measure to the irregularity, but this is 

 hardly a likelihood. We have referred to the bacterial con- 

 tamination of one series of cultures, with the consequent reduction 

 in weight of the pupse. Curiously enough, this reduction in 

 weight does not appear to have induced a parallel modification 

 in rate of metabolism. 



The pupae of Drosophila, it would seem, are adapted to resist 

 conditions of desiccation, at any rate for short periods. On 

 several occasions lots of pupae were inadvertently subjected 

 overnight to the drying effect of the room air. This treatment 

 produced no detectable effect on the following day either in 

 pupal weight or in rate of oxygen consumption. This point is 

 of some interest in connection with the results obtained by 

 Caldwell (1925), who has found that the metabolism of some 

 animals, as measured by carbon dioxide production, is modified 

 as a result of desiccation. 



A degree of irregularity in oxygen rates was certainly intro- 

 duced with varying ages of the pupae used. Larvae developing 

 from eggs deposited on a single day possess individual peculiar- 

 ities, some pupating precociously, others delaying the act for a 

 day or longer after their brothers and sisters have made the 

 change. Accordingly, all of the pupae thrown together for a 

 determination are not of the same age. Among lots of experi- 

 mental pupae, however, the mean ages should be nearly identical 

 as selection was performed at about the same hour each morning 

 and the manometer readings were distributed over approximately 

 identical time periods each day. 



Mention might be made of an attempt to find an interpretation 

 of the irregularity in rates through a study of varying intensities 

 of such environmental factors as light, humidity, etc., data for 

 which were secured from the local weather office. As might be 

 expected, this attempt was not fruitful of results. Likewise, a 



