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



The average effect of all these reagents upon the resistance to 

 cyanide, if such is worth anything, shows no marked difference 

 between positive and negative treated animals nor between the 

 treated animals and the control. 



From these experiments with Leptophlebia we have the inter- 

 esting results that these nymphs were reversed without affecting 

 their resistance to potassium cyanide (HCl and averaged results) ; 

 with accompanying stimulation (alcohol) and with accompanying 

 depression (chloretone). 



The quantitative reversal of positive Epeorus nymphs and 

 negative Leptophlebia by 1 per cent alcohol in the same ex- 

 perimental dish at the same time was repeatedly demonstrated. 

 Thus conditions absolutely identical caused opposite reversals 

 in the two species. At first sight this would appear to mean that 

 both positive and negative animals were reversed for the same 

 reason. This is not necessarily true. In the tests to find the 

 strength of potassium cyanide that would directly measure the 

 metabolic rate of the two species it was found that Leptophlebia- 

 was only one-fourth as sensitive as Epeorus. Since the Lepto- 

 phlebia are much more resistant, a strength of alcohol that only 

 stimulated them may have clearly depressed Epeorus. That 

 such is the true explanation is indicated by the effect of alcohol 

 on the resistance of the two species of nymphs to cyanide. The 

 Epeorus that had been made negative were found to be depressed, 

 while the Leptophlebia that were made positive were clearly 

 stimulated. 



II. REVERSALSOF PHOTOTAXIS AND CARBON DIOXIDE PRODUCTION "'^ 



METHODS 



The experiments upon which the second part of this report 

 is based were carried on at Lake Forest College upon a May-fly 



^ This section is based on experiments by the senior author, now being 

 continued, which were started in the spring of 1916. They were made possible 

 by money grants from the Elizabeth Thompson Fund and from the Bache Fund 

 of the National Academy. 



3 The nymph whose reactions are described in the second part of this paper is 

 Heptagenia pulchella Walsh. We are indebted to Professor J. G. Needham for 

 this identification. 



