336 



MOTOR RESPONSES 



movement. On the other hand, there are some very definite results con- 

 cerning the relation between the rate of locomotion and the chemicals in 

 the surrounding medium, especially hydrogen ions. 



Rate of locomotion and H-ion concentration. — Hopkins (1928) ob- 

 served that A. proteus, in an ordinary hay culture fluid, is inactive if the 

 fluid is neutral, but active if the fluid is either acid or alkaline, and that 

 the rate of locomotion is maximum and nearly equal at about pH 6.5 



Z60 





ptl 



Figure 121. The relation between rate of locomotion, gel/sol ratio, hydrogen-ion con- 

 centration, and calcium-ion concentration. Curve O, mean rate of locomotion in 0.001 M, 

 based on measurements on an average of 22.1 different specimens for 11.6 minutes in 

 each hydrogen-ion concentration tested; curve #, mean rate of locomotion in 0.005 M, 

 based on an average of 18.7 different specimens for a total average of 96.6 minutes in 

 each hydrogen-ion concentration tested; curve 3, mean gel/sol ratio in 0.001 M, based 

 on measurements on an average of 21.3 different specimens in each hydrogen-ion con- 

 centration tested; curve O, mean gel/sol ratio in 0.005 M, based on measurements on 

 a total average of 14.6 different specimens in each hydrogen-ion concentration tested. 

 (After Pitts and Mast, 1934b.) 



and pH 8 respectively. Mast and Prosser (1932) confirmed these results. 

 Pitts and Mast (1933), in a much more thorough study on A. proteus, 

 demonstrated that the inactivity at neutrality is correlated with the rela- 

 tion between the amount of sodium or potassium and calcium present; 

 and that the relation between activity and the concentration of hydrogen 

 ions varies greatly with the kind, the concentration, and the proportion 

 of salts in the surrounding medium. Some of the results obtained in this 

 study are presented in figures 119, 120, 121, and 122. These figures 

 show the following: 



