LIGHT EEACTIONS METABOLISM — MAY-FLY NYMPHS 429 



DOES RESISTANCE TO POTASSIUM CYANIDE MEASURE THE RATE OF 

 METABOLISM IN MAY-FLY NYMPHS? 



In this work the cyanide resistance method of Child ('13) was 

 used without modification except in the strength of the cyanide 

 solutions employed. In this method with a relatively high 

 concentration the animals with a higher rate of metabolism 

 (cf. Geppert, '99, Hyman, '16) die before those with a lower rate. 

 In much weaker solutions acclimatization occurs and the effect 

 is reversed. The resistance of the nymphs was tested in 500-cc. 

 Erlenmeyer flasks. Control experiments showed that the more 

 sensitive Epeorus nymphs could live from five to fifteen days in 

 this amount of unchanged tap water, provided the temperature 

 was approximately constant. 



Some difficulties were encountered in determining the death 

 point. The nymphs were usually observed every thirty minutes 

 in later experiments every twenty minutes) , and those that were 

 apparently motionless were removed with a large pipette and care- 

 fully inspected under a lens. If no motion was apparent they 

 were stimulated with a needle. If they failed to show any mo- 

 tion under these conditions they were considered dead. It is 

 obvious that this treatment would stimulate live nymphs and 

 more frequent inspection would increase rather than decrease 

 the experimental error. 



Epeorus proved to be much less resistant to the cyanide than 

 Leptophlebia. With the former (table 1) a solution 0.00001 

 normal gave a measurement of metabolism by the 'direct 

 method;' with the latter the same measurement was obtained 

 by a strength of 0.0025 normal. With Epeorus 0.000001 normal 

 was found to measure metabolism by the acclimatization 

 method. With this dilution so great care was necessary in 

 order to maintain the solution at even its approximate strength 

 that no serious tests were run. 



A new solution of 0.1 normal potassium cyanide was made 

 up weekly, and from this dilutions were made to the desired 

 strength. With extreme dilutions and with certain preliminary 

 experiments which ran several days the solutions were made 

 up fresh twice daily. 



