CONTROL OF RHEOTAXIS IN ASELLUS 189 



give the best evidence obtainable as to whether or not a change 

 in the metabohc state accompanied the increase in positive- 

 ness. The extent of rheotactic change is shown in part I of 

 table 5. Of the 49 isopods tested only one had its positiveness 

 decreased by the 7-28 minute treatment with N/^IO solution. 

 The average rheotactic response was increased from 10 to 74 

 per cent positive. Comparison of the survival time with that 

 shown in part II gives the effect of the treatment with potas- 

 sium chloride upon the susceptibility to N/400 sodium cyanide. 

 The resistance of 19 highly negative, untreated isopods was 6.1 

 (±0.3) hours and of the 49 untreated isopods 4.12 (±0.2) 

 hours. The difference is approximately two hours which is 

 four times the probable error and therefore statistically 

 significant. 



These results are also graphically shown in figure 10 in which 

 the solid line gives the resistance of the 49 isopods after being 

 made positive with potassium chloride and the broken line 

 gives that of the 19 untreated animals. The height above the 

 base line gives the number of isopods dying each hour. The 

 vertical lines again show averages and the double pointed arrows 

 give the extent of the probable error. 



Effect of calcium chloride upon resistance to cyanide and upon 

 carbon dioxide production 



Opposed to potassium chloride, calcium chloride was the 

 most effective depressing salt found. Its effect on the metabolic 

 rate may be judged both by its effect on resistance to cyanide 

 and on carbon dioxide production. 



Seventy-one highly positive isopods were treated with cal- 

 cium chloride long enough to cause a reversal in rheotaxis and 

 then gave a resistance to N/400 sodium cyanide of 6 hours 34 

 minutes ( ± 4 min.) while 27 highly positive, untreated isopods 

 gave an average resistance to the same strength of cyanide of 

 5 hours 32 minutes ( ±13 min.) The difference here is 3.7times 

 the probable error. It was not thought necessary to carry 

 this series further because of work done with Dr. Tashiro (Allee 



