340 MOTOR RESPONSES 



above, even less explicable than are those in reference to the gel/sol ratio. 

 The outstanding difficulty here concerns the remarkable decrease in rate 

 of locomotion as neutrality is approached either from the acid or from 

 the alkaline side. The results presented show that this decrease occurs in 

 balanced solutions; that is that it is specifically correlated with the Na/Ca 

 ratio; that the higher this ratio within the limits of the concentrations 

 tested, the greater the decrease; and that it does not occur in solutions con- 

 taining only one salt. . . . 



The results show that if calcium is added to a solution containing only 

 sodium salts, the rate of locomotion in the alkaline range increases greatly, 

 with but little change in the acid range and in the region of neutrality ; and 

 that if sodium is added to solutions containing calcium salts, the rate de- 

 creases greatly in the region of neutrality, with but little change else- 

 where. . . . 



The questions now arise as to why addition of calcium to solutions con- 

 taining only sodium salts causes great increase in rate of locomotion in the 

 alkaline range, and why addition of sodium to solutions containing only 

 calcium salts causes great decrease in the rate in the region of neutrality. 



Similar questions have arisen in reference to the bimodal curves obtained 

 by a number of other investigators in plotting the rate of various physiological 

 processes against hydrogen ion concentration, e.g., by Robbins (1926) and 

 Farr (1928) in various processes in plants; by Ephrussi and Neukomm 



(1927) in the resistance to heat in the eggs of a sea urchin; by Hopkins 



(1928) in the rate of locomotion in A>?ioeba; by Mast (1928) in the rate of 

 assumption of stellate forms in Amoeba; by Eisenberg-Hamburg (1929) in 

 the rate of increase in water content in infusoria; by Chalkley (1929) in 

 water content and gel/sol ratio in Amoeba; and (1930a, 1930b) thermal 

 death rate in Paravieciiim ; by Chase and Glaser (1930) in rate of locomo- 

 tion in Paramecium : and by Mast and Prosser (1932) in rate of locomotion 

 in Amoeba. . . . 



Only a few of these investigators attempted to elucidate the phenomenon. 

 Mast and Prosser (1932), as previously stated, concluded that it is cor- 

 related with salt concentration. We have already considered this view. 

 Robbins (1926) contends that the hydrogen ion concentration, at which the 

 median minimum in the plant processes studied occurs, coincides with the 

 isoelectric point of the principal proteins in the plant. Farr (1928) main- 

 tains, however, that this view is not tenable. He found in observations on 

 the relation between hydrogen ion concentration and rate of growth in root 

 hairs of collards that the hydrogen ion concentration at which the median 

 minimum occurs varies greatly with salt concentration and he concludes that 

 it therefore cannot be specifically correlated with the isoelectric point of 

 any given protein in the organism. . . . 



In reference to Amoeba, the constancy of a median minimum rate of 



