A STUDY OF OXYGEN METABOLISM, j 451 



reduced until, on the third day, the normal balance of respiring 

 and non-respiring materials was restored. The first determina- 

 tion, number 8, on the other hand, presents a different story 

 which is complicated by the fact that 5 of the 10 pupae on which 

 this determination is based failed to complete their development, 

 the only case of the sort we shall consider. The approximation 

 of the metabolism curves suggests that the pupae contained a 

 very small amount of non-respiring material relatively to the 

 respiring tissues, yet this idea does not seem to harmonize with 

 the remarkable fall in pupal weight occurring after the first day 

 of pupal life. If, however, we postulate for this case, as was done 

 earlier for cases of arrested development in general, a bacterial 

 activity which would serve to elevate the metabolism per unit 

 body weight relatively to the total metabolism, we develop an 

 interpretation which affords an understanding not only of the 

 peculiar relation shown by the two curves but also of the cause 

 for the unusual decrease in pupal weight. Instances of this 

 sort, representing a fluctuation in the relative amounts of re- 

 spiring and non-respiring substances present in pupae, are of 

 frequent occurrence and are further illustrated in Fig. 5. The 

 only general statement that seems permissible is that pupae of 

 very low weight usually show an elevation of the rate per unit 

 weight relatively to the total metabolism but this condition is 

 by no means invariably true. It appears, therefore, that mere 

 weight is a rather unreliable index of the amount of respiring 

 tissue. 



It is manifest that for the first and second days of pupal life 

 a rough proportionality certainly exists between pupal weights 

 and metabolism, thus explaining in a way the trends of the 

 oxygen curves. However, the peculiarities of the I2th, i6th and 

 iQth determinations must receive an interpretation of their own. 

 As the two metabolism curves remain closely parallel, the only 

 conclusion that seems justifiable is that the rates for the deter- 

 minations in question are of a discontinuous type; in other words, 

 independent of pupal weight. It would appear, therefore, that 

 strictly comparable samples of respiring tissue grown under, and 

 subjected to, like environmental conditions can nevertheless 

 exhibit marked diversity in rates of metabolism. It is ex- 



