CONTROL OF RHEOTAXIS IN ASELLUS 



171 



monium salts may be eccentric in their action and Mathews 

 interprets this as due largely to their hydrolytic dissociation 

 but this explanation is unsatisfactory so- far as the present work 

 is concerned because of the slight amount of this kind of dis- 

 sociation in the solution strengths used. 



Fig. 2 Showing relative toxicity and the relative effect of different anions 

 with the cation potassium on positive rheotaxis of Asellus. For details see text 

 p. 172. 



Different anions with the cation potassium 



Some work was carried on to find whether different anions 

 with the most effective cation, potassium, also affected rheotaxis. 

 The studies were only carried far enough to demonstrate that 

 the anions are effective and to suggest in a tentative way the 

 order of their relative effect. The findings with N/10 solutions, 

 which was the strength most often used, are shown in figure 2. 



Figure 2 is charted in much the same manner as the preceding 

 figure. The anions are arranged in their usual relative colloidal 



