174 W. C. ALLEE 



solutions of barium, calcium and magnesium chlorides and of 

 N/5 solution of strontium chloride, together with their effect 

 on positive rheotaxis. The different columns have the follow- 

 ing significance: No. 2 shows the number of isopods on which 

 the toxicity time was determined; No. 3 gives the average toxic- 

 ity; No. 4 gives the ratio of toxicity -depression in percentages of 

 the toxicity time; No. 5 lists the number of rheotactic tests 

 made whose results are shown in the next two columns; No. 6 

 shows the percentage of isopods that showed some increase in 

 rheotactic positiveness during the treatment and the last column 

 gives the amount of the increase or decrease at the most positive 

 period of treatment. 



Strontium chloride is decidedly more toxic than any of the 

 others; barium comes next and after an interval comes calcium 

 with magnesium much the least toxic. Calcium chloride at 

 M/5 concentration failed to give a preliminary increase in the 

 positive rheotaxis but it did cause an increase in 5 per cent of 

 all the trials made at all concentrations. Calcium also caused 

 a marked decrease in positiveness even when the most positive 

 responses are considered. The low percentage shown by the 

 ratio of depression to toxicity indicates that unlike potassium 

 and rubidium the depression is not due primarily to toxicity. 



Strontium chloride acts much as calcium chloride except that 

 it is less effective in the concentration used and more toxic. 

 Although magnesium stimulated approximately one-third of 

 the isopods during the first 45 minutes of treatment the 

 average effect of the treatment was a decrease in positiveness. 



Barium chloride caused a greater initial stimulation than 

 any other chloride tried excepting only those of potassium and 

 rhubidium and possibly sodium. In percentage of individual 

 stimulated, in amount of stimulation, and in the relatively high 

 toxicity-depression ratio barium aligns itself with the alkali 

 metal group. This is in keeping with its usual physiological 

 action which has been known since Ringer ('86) found that it 

 acted mth the alkali metals rather than as the other alkali 

 earths. 



