A STUDY OF OXYGEN METABOLISM. 445 



leading to their ultimate dissolution, and that the tissues of the 

 imago are built up through the activity of certain groups of 

 cells which survive histolysis and appear to be set aside for this 

 specific purpose. In other words, two distinct processes are in 

 progress during pupal life a destructive and a constructive, the 

 latter being inaugurated before the completion of the former. 

 The authors cited identify the abrupt fall in metabolism early 

 in pupal life with the histolytic process and the recovery after 

 the period of depression with the formation and growth of 

 imaginal tissues. 



VARIABILITY IN RATES OF METABOLISM. 



When a series of curves for rates of oxygen consumption is 

 examined, a feature which is most striking is the considerable 

 variability in values exhibited. The majority of the values for 

 any one day of pupal life fall within fairly narrow limits, but 

 scattered among these are numerous others representing very 

 high as well as rather low rates, distributed in a seemingly erratic 

 manner. An early examination of the data proved that most of 

 the very high rates belonged to lots of pupae, one or more members 

 of which not only failed to give issue to flies but failed to pass 

 beyond the stage of development characteristic of second day 

 pupae. Instances of this sort suggest that probably intestinal 

 microorganisms find their capacity for growth released by the 

 death of the pupa or pupae harboring them, and by their rapid 

 multiplication elevate the rate of oxygen consumption to a high 

 level. With one exception to be considered later, it w r as deemed 

 necessary to completely eliminate from further consideration all 

 data pertaining to lots of pupae showing incomplete development, 

 thereby reducing the total number of determinations by about 

 one third. Several further eliminations are for lots of pupae 

 which were accidentally shaken from their supports within the 

 manometers into the 2 per cent. NaOH solution over which they 

 were suspended. Although washed as quickly as possible in a 

 large volume of water and again set up in the manometer, a lot 

 so treated almost invariably responded with an abnormal eleva- 

 tion of rate. Mention should also be made of a series of deter- 

 minations which was set aside because of bacterial contamination 



