MOTOR RESPONSES 



337 



In a balanced salt solution the activity is minimum at neutrality and 

 maximum on either side; but the activity at any given hydrogen-ion 

 concentration varies with the salt concentration (Fig. 119). In sodium 

 or calcium salt solutions (Table 2) the maximum rate of locomotion 

 is nearly as high as in a balanced salt solution. Furthermore, the rate at 



Figure 122. The effect of adding calcium in different concentrations to 0.005 N sodium 

 solutions, on the relation between hydrogen-ion concentration, rate of locomotion, and 

 gel/sol ratio. The solid curve for the solutions containing calcium 0.001 M is based 

 on measurements of the rate of locomotion, on an average of 14.75 different specimens 

 for a total average of 89.9 minutes; that for calcium 0.0005 M, on an average of 18.6 

 different specimens for a total average of 95 minutes; and that for calcium 0.001 M, on 

 an average of 20.5 different specimens for a total average of 104.6 minutes in each 

 hydrogen-ion concentration tested. The broken curve for the solution containing cal- 

 cium 0.001 M is based on measurement of the gel/sol ratio, on an average of 19.8 

 different specimens; that for calcium 0.0005 M, on an average of 17.9 different speci- 

 mens; and that for calcium 0.0001 M, on an average of twenty different specimens in 

 each hydrogen-ion concentration tested. (After Pitts and Mast, 1934c.) 



any given hydrogen-ion concentration varies with the salt concentration, 

 although the relation between the rate and the hydrogen-ion concen- 

 tration in the one differs greatly from that in the other, and there is no 

 indication of inactivity at neutrality in either (Figs. 120, 121). If cal- 

 cium salt is added to a solution of sodium salt, the activity decreases 

 greatly at neutrality (Fig. 122). The ratio between the amount of plas- 

 magel and the amount of plasmasol in Amoeba varies with the hydro- 

 gen-ion concentration; but the rate of locomotion is not specifically cor- 

 related with this ratio. 



