158 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



There is no noticeable difference in the color or melting points of fats 

 from 17° and 25° larvae. The ether extract is a brownish amber and begins 

 softening at about 30° but does not fully melt until 50-55°C.^ The debility 

 is certainly not caused by exhaustion of total food reserves because larvae 

 from eggs incubated at 17° still have about half the original fat of the egg 

 and a large amount of the albuminous yolk. Even after incubation at 15° 

 the larvae contain some fat and considerable albuminous yolk (fig. 8). 

 These gross determinations, however, do not exclude the possibility that 

 the important factor may be exhaustion of some specific component in the 

 stored reserves. To test this, several lots of larvae from eggs incubated at 

 17° were induced to feed on solutions containing glucose, a mixture of known 

 vitamins, yeast or casein, or a mixture of all of these (in addition to the 

 availability of milkweed seeds) . The low percentage survival was no better 

 on these fortified diets than in the controls reared under standard culture 



0.5 



I 0.4 



0.3- 



6 0.2- 



e 



0.1 



Fig. 10. Oxygen consumption 

 of freshly hatched Oncopeltus 

 larvae incubated at 17° (open 

 circles) and 25° (solid circles). 

 A, values of curve C corrected 

 to a comparable weight basis by 

 multiplying by 1.1; B and C, 

 average O2 consumption per 

 larva. 



15 



20 



25 



30 °C. 



conditions. Since we were not successful in inducing vitality by this means, 

 I doubt that the debility has a nutritional deficiency basis. 



The conclusion that the debility does not have a nutritional basis is sup- 

 ported by the finding that larvae from eggs incubated at 25° gradually die 

 off when reared at 17°C. From 257 larvae, a single male adult was obtained 

 after 103 days; yet these larvae fed on the normal culture food. Inciden- 

 tally, the single adult obtained was one which had spent its entire growth 

 ])eriod (125 days) at 17° ; none of the 177 larvae from eggs incubated at 25° 

 survived past the last larval instar. 



The debility also does not have the aspect of having a hormonal basis. 

 To be such, the hormone would have to be a general growth promoter 

 present from fairly early embryonic stages (not later than the time when 



* This contrasts with the ether extract from freshly laid eggs. Egg fats are a yellow 

 amber and fluid at room temperature. But we do not know whether this difference 

 indicates a metabolic change or only a changing proportion due to the production of 

 cuticular waxes. 



