ACCLIMATION IN PLANARIA DOROTOCEPHALA. 283 



that cyanides decrease the activity of oxidizing enzymes. Hy- 

 man ('16) has recently shown that in all except very low con- 

 centrations cyanides decrease oxygen consumption in the sponge. 

 I am also permitted to mention the results of recent experiments 

 on Planaria dorotocephala not yet published: Dr. Hyman shows 

 that here also cyanides decrease oxygen consumption to a 

 marked degree, and Professor Child has been able to demonstrate 

 a parallel decrease in CO 2 production in the same material under 

 the influence of cyanides. This action of KNC upon oxidation 

 makes it very effective for the purposes of these experiments, 

 since metabolic rates are best measured in terms of oxidative 

 processes. And Child ('130) has presented evidence of the fact 

 that susceptibility to cyanide increases with rise in temperature, 

 so there is good precedent for the use of this agent. 



The concentration of KNC found most effective was a I/ 1,000 

 molecular solution made up with water of the appropriate tem- 

 perature. In each lot 10 worms of as nearly as possible the same 

 size were used. They were put in a 100 c.c. Erlenmeyer flask, 

 the water drained off and the worms then rinsed in the appro- 

 priate cyanide solution (made up fresh each time), after which 

 the flasks were filled and stoppered tightly to prevent loss of 

 KNC by evaporation. The method of recording death rates 

 was that employed by Child ('15) in which certain arbitrarily 

 defined stages in the course of disintegration were distinguished 

 as follows: 



Stage I. The worm is still intact. 

 Stage II. The first signs of disintegration are apparent. These 



usually appear at the head end but, as we would 



expect, also very soon in the region of the posterior 



zooids. 

 Stage III. The beginning of disintegration on the margins 



posterior to the head. 



Stage IV. Margins completely disintegrated. 

 Stage V. There is no tissue left with any appearance of life. 

 From the data thus obtained graphs were plotted by the 

 method that Child has previsouly used ('15, p. Si). 1 



1 T his method consists in giving numerical values to the stages of disintegration 

 as follows: Stage II., i; Stage III., 2; Stage IV., 3; Stage V., 4; and using as 



