CONTROL OF RHEOTAXIS IN ASELLUS 195 



Since the most efficient stimulating and depressing salts 

 found affect the metabolic rate of the isopods as measured 

 by their resistance to the cyanides and (calcium) by carbon 

 dioxide production the results of these experiments support 

 earlier work on this subject which demonstrated that Asellus 

 with a high rate of positive rheotaxis have a relatively high rate 

 of metabolism and those with a low degree of positiveness tend 

 to have a low rate of metabolism. Lillie ('09) gives evidence* 

 to show that the primary action of pure sodium and potassium 

 chloride solutions is to increase, and that of magnesium and 

 calcium chlorides, to decrease permeability in Arenicola larvae 

 and that these stimulate and depress, respectively, the muscular 

 activity of these animals. He concludes that this increase in 

 permeability is in itself sufficient to account for the liberation 

 of energy which is the essential consequence of stimulation. 

 Whether or not the relationship between these salts and rheo- 

 taxis can be fully explained on such a basis is a matter for fur- 

 ther experimentation. 



V. SUMMARY OF EXPERIMENTAL RESULTS 



The chlorine salts of the alkali metals affect the rheotactic 

 reaction of Asellus communis in such a way as to suggest that 

 there is a relation between the chemical activity of these cat- 

 ions and their effect on rheotaxis of isopods. Potassium is 

 the most effective in increasing the positiveness of the reaction, 

 with rubidium a close second, p. 167. 



The relative toxicity of these cations does not run parallel 

 with their stimulating power but resembles the relative favor- 

 ableness in preserving the activity of frog nerves and muscles 

 p. 170. 



The anions of the most stimulating cation, potassium, affect 

 the rheotactic reaction but their effectiveness does not run 

 parallel with their chemical activity and the relative toxicity, 

 while similar, is not exactly the same as the stimulating power, 

 p. 172. 



Any chemical in the concentrations used will cause a decrease 

 in the positive rheotactic reaotion, but the chlorine salts of 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 21, NO. 2 



