282 ELLINOR HELENE BEHRE. 



the metabolic rate is so high that it is difficult to keep stock 

 sufficiently nourished to allow it to increase in size. The worms 

 are restless, and soon become thinner, narrower and much lighter 

 in color. For example, a stock collected November 17, 1917 

 and set in the warm chamber January u, 1918 at average 

 temperature of 27.5 was fed tri-weekly. The reduction in size 

 was rapid; the worms originally 15-18 mm. in length decreased 

 within a period of two weeks to 9-10 mm., and were very much 

 more slender than the worms of the same stock and size in the 

 same temperature under daily feeding. It was further noticed, 

 though no measurements were taken, that this reduction was 

 more rapid, even, than in a parallel starvation stock at lower 

 temperatures ranging from 14-16. That these differences in 

 appearance and behavior are directly associated with the meta- 

 bolic rate needs no further proof. Even the pigment changes 

 cannot be a matter of kind of food but must, it seems, be related 

 to oxidation rate in some such way as the alterations in pigmenta- 

 tion which cause seasonal dimorphism in butterflies (Dorfmeister, 

 1879, Weismann, 1895, et al.). 



IV. RELATION OF SUSCEPTIBILITY TO TEMPERATURE CHANGES. 



The experiments to be reported in this section deal with altera- 

 tions of metabolic rate in acclimation as tested by the suscepti- 

 bility method. This method as devised by Child ('i3a) consists 

 in subjecting the animals to concentrations of certain agents 

 which will kill them slowly enough to permit one to observe 

 accurately differences in their time of death. Child has suffi- 

 ciently demonstrated that the time required for death is de- 

 pendent upon metabolic rate, being shorter the higher the rate. 

 Therefore in my experiments I have used the time required for 

 death as a measure of the effect of various conditions of tempera- 

 ture upon the metabolic rate. 



In all the experiments reported here, KNC was the agent 

 used. The work of earlier physiologists, notably that of Geppert 

 (1889), demonstrated that the action of KNC on vertebrates in 

 some way prevents the tissues from utilizing the oxygen of the 

 blood. Loeb and various other more recent workers have used 

 KNC extensively to inhibit oxidations; and it has been shown 



