CONTROL OF RHEOTAXIS IN ASELLUS 193 



and Tashiro '14) upon the effect of calcium chloride upon car- 

 bon dioxide production in Asellus. A part of these results 

 are republished here: 



In brief the experiments were as follows : Two isopods of approxi- 

 mately the same size were tested for their relative rate of carbon diox- 

 ide production in the Biometer. The isopod having the lower rate 

 of carbon dioxide output was taken as a control and was again tested 

 for the rheotactic reaction and then left in conditions to which it was 

 acclimated while the other was treated. The second individual 

 which had the higher rate of carbon dioxide production was placed in 

 a 0.2 mol. solution of calcium chloride until the tendency to give a 

 positive rheotactic reaction was markedly reduced. Then the rate 

 of carbon dioxide production of the two was again tested in the 

 Biometer. 



In both pairs tested the isopod with the higher rate of carbon dioxide 

 production at the first test in the Biometer had also given the higher 

 percentage of rheotactic responses, but after being treated with cal- 

 cium chloride for 25 to 36 minutes it came to be less positive in its 

 rheotactic reaction, and also gave less carbon dioxide and was less 

 susceptible to potassium cyanide than the control individual. In other 

 words the calcium chloride (0.2 mol.) decidedly decreased the rate of 

 metabolism of the isopods and alsa reduced their tendency to give a 

 positive rheotactic reaction. 



Effect of cane sugar on resistance to potassium cyanide 



Fifty-four isopods that gave an original average rheotactic 

 response 33, 54, 9, 1 per cent positive, negative, indefinite, and 

 zero were treated with M/2 cane sugar until they gave an average 

 reaction of 18, 24, 52, 6. Forty-eight of these were immediately 

 killed in N/1000 potassium cyanide and gave an average survival 

 time of 8 hours 23 minutes ( ±31 min.). ' Eighty -six isopods that 

 gave an average rheotactic response of 34, 57, 9 per cent respec- 

 tively resisted the same strength of cyanide for an average of 

 5 hours (±7 min.). This is a difference of 3 hours 23 minutes 

 which is over five times the probable error and undoubtedly 

 significant. Since the cane sugar probably acted by removing 

 water (Peters '04 for Stentor) we have here excellent evidence 

 that such conditions depress the rate of oxidations in Asellus 

 which corresponds to the results reported by Riddle ('14) for 

 the pigeon's egg. 



