METABOLISM OF INSECTS 



549 



The starvation experiments were also 

 carried on at Z2.°C, and the results showed 

 that the carbon dioxide output decreased 

 during the first week of starvation, but in 

 each set of insects the output increased 

 during the second week. The explanation 

 of this increase is questionable. It may 

 be that at this stage the nymph draws 

 heavily on its reserve food or on its 

 tissues. During the third and fourth 

 weeks, the animals showed a steady 

 decrease in metabolic rate. Nearly all the 

 starved nymphs died before the seventh 

 week, although two lived two months 

 without food. In comparing the results 

 of the starvation experiments with those 

 of the controls, one could observe that the 

 carbon dioxide output of a starving insect 

 decreases in one week by an amount com- 

 parable to the decrease in twenty days in 

 a younger insect and to ten days in the 

 older animals. At the end of four weeks 

 of starvation, the carbon dioxide output 

 was about the same as the output of the 

 controls at the end of three months. It 

 was interesting also to note an increase in 

 weight in the starving insects. Since the 

 nymphs are aquatic, this increase was 

 probably due to the replacement of reserve 

 fat by water during starvation. 



The effect of darkness on carbon dioxide 

 output is shown in figure z. The me- 

 tabolic rate decreased progressively with 

 the weeks of darkness up to the sixth 

 week, when four individuals died. Al- 

 though the experiment was then brought 

 to a close, the remaining nymphs were 

 kept in the dark until all died, which 

 occurred within a period of two weeks. 

 That the metabolic rate of these animals 

 is decreased by darkness can readily be 

 seen by comparing the data here given 

 with the data obtained from the controls. 

 Per unit of weight the C0 2 output of the 

 nymphs was much less than that of the 

 control animals. A control insect weigh- 



ing 0.Z14 grams gave ofFo.6499 milligrams 

 of C0 2 per hour, while an insect in dark- 

 ness weighing o.zn grams produced only 

 0.Z345 milligrams. 



Since most of the animals lived but six 

 or seven weeks, the decreased C0 2 pro- 

 duction must have been accompanied by a 

 pathological condition resulting in early 

 death. It is evident that light is neces- 

 sary for the normal physiological proc- 

 esses, and that a lack of it produces an 

 abnormal condition bringing about death. 

 It would be interesting in further research 

 to determine what part of the spectrum is 

 of greatest importance in the normal life 

 of these nymphs. 



Figure 3 represents the average amounts 

 of carbon dioxide given off by three sets 

 of insects as the temperature of the water 

 in which they were living was gradually 

 raised. Most of the authors already 

 cited determined the C0 2 output at each 

 increase in temperature without making a 

 study of the metabolic rate after a longer 

 exposure to the same temperature. In- 

 stead of making the usual successive de- 

 terminations at different temperatures, 

 three determinations were made at each 

 temperature. These records were made 

 after twenty-four, forty-eight, and 

 seventy-two hours exposure to the given 

 temperature. In following this plan, a 

 different curve was secured than is usually 

 drawn. Reference to the graph shows 

 that the C0 2 output goes up for each tem- 

 perature after the twenty-four hours of 

 exposure, but goes down again after the 

 longer periods of exposure. The output 

 is about normal after seventy-two hours 

 at the given temperature. These results 

 were found to be true in the case of each 

 rise in temperature. If one connected 

 with a line the twenty-four hour points 

 on this graph, the usual rising curve 

 could be secured. However, according to 

 the method of determination followed 



