196 W. C. ALLEE 



calcium and strontium cause this decrease usually without a 

 preliminary stimulation. Magnesium chloride while in the 

 main similar in action often causes preliminary stimulation 

 and barium chloride is still more stimulating, resembling the 

 alkali metals in its effect, p. 173. 



In the cations such as potassium which are highly stimulat- 

 ing the depression is a toxic effect while in depressing cations 

 as calcium, rheotaxis is depressed long before toxicity symptoms 

 appear, p. 174. 



There is a marked antagonism between the effect of potassium 

 and calcium chlorides and a less marked one between the chlorides 

 of sodium and magnesium, p. 175. 



Both acids (H ions) and alkahes (OH ions) in the concen- 

 trations used generally decrease the percentage of positive re- 

 sponses given, p. 177. 



Once distilled water gave some evidence of causing Asellus 

 to become more positive in their rheotactic reaction, though 

 pure water was quite toxic, p. 181. 



Cane sugar decreased the positive rheotactic reaction probably 

 by extracting water and the action of the once distilled water 

 may be due to water intake, p. 183. 



The results obtained with salts are not osmotic effects be- 

 cause equimolecular solutions of different salts with approxi- 

 mately the same osmotic pressure may have opposite effects 

 and because cane sugar in M/2 solution was a less effective 

 depressant than N/10 calcium chloride although its osmotic 

 pressure is over three times as great, p. 185. 



Susceptibihty to sodium cyanide N/400 or N/500 measures 

 the rate of metabolism of Asellus probably by limiting the oxy- 

 gen consumption, p. 188. 



Measured in this way, potassium chloride when increasing 

 positive rheotaxis also increases the rate of isopod metabolism, 

 and calcium chloride and cane sugar decrease both positive 

 rheotaxis and the metabolic rate. Calcium chloride also de- 

 creases the carbon dioxide output, p. 189. 



