430 W. C. ALLEE AND E. R. STEIN, JR. 



The inquiry as to whether resistance to potassium cyanide in 

 May-fly nymphs is affected by the rate of metaboHsm of the ani- 

 mal was prosecuted along the following lines : 



1) What is the relation between the resistance of large (old) 

 and small (young) nymphs? 



2) What is the effect of stimulation upon the resistance to 

 the cyanide? 



3) What is the effect of differences in temperature? 



The results of these experiments are summarized in table 1. 

 Nymphs of Epeorus were less resistant to 0.00001 normal potas- 

 sium cyanide when they were small, or stimulated, or at increased 

 temperature. All of these conditions cause a higher rate of 

 metabolism (Child, '13; Allee, '14). On the other hand, in a 

 0.000001 normal solution the smaller (younger) nymphs were 

 more resistant than the larger ones, which is what the theory 

 demands if a solution of this strength to measure indirectly the 

 rate of metabolic processes. 



Leptophlebia in 0.0025 normal solution was less resistant when 

 young, or stimulated, or when the temperature was increased 

 so that this strength of cyanide directly measures the metabolic 

 rate of these nymphs. A solution 0.00025 did not indirectly 

 measure the rate of metabolic processes of these nymphs and 

 the experiments were not continued long enough to find a solu- 

 tion strength that would do so. In all the above instances in 

 which the evidence is that cyanide resistance does measure 

 the rate of metabolism the differences in the survival times 

 exceeds twice the probable error and we may safely hold them 

 to be statistically significant. 



RELATION BETWEEN THE SIGN OF LIGHT REACTION AND RESIST- 

 ANCE TO THE CYANIDE 



1. Epeorus 



The average survival time of fifty-one positive Epeorus 

 nymphs (table 2) which had been taken directly from tap water 

 was 108 =±= 5 minutes. These nymphs averaged 5.4 mm. long. 

 A reversal of the phototactic reaction of forty-seven other posi- 



