MOTOR RESPONSES 315 



forming acids (e.g., HCl). The cathodal surface layer of the amoebae 

 should therefore become alkaline on the inside and acid on the outside. 

 The anodal surface layer should react in the opposite manner. 



Numerous observations were made on specimens stained with neutral 

 red and subjected to direct current under various conditions. No differ- 

 ence whatever was observed in the color of different regions in any of 

 these specimens. The neutral red staining in A. proteus is, however, 

 confined to granules and vacuoles. It was observed that if the specimens 

 are crushed, the color of these granules and vacuoles does not immedi- 

 ately change, in accord with the hydrogen-ion concentration of the solu- 

 tion in which they are immersed. It is obvious, then, that the fact that 

 no difference in color was observed in the vacuoles and granules does not 

 prove that the hydrogen-ion concentration of the cytoplasm was the 

 same. Moreover, there is indirect evidence which indicates that it was 

 not the same. 



Kiihne (1864) long ago observed in certain epidermal cells of the 

 leaves of Tradescantia subjected to a galvanic current that the ends of 

 the cells directed toward the cathode become alkaline, and that those 

 directed toward the anode become acid. These cells contain a natural 

 indicator which is bluish in neutral solutions, red in acid solutions, and 

 green in alkaline solutions. 



Habenicht (1935) came to the same conclusion in experiments on the 

 effect of the galvanic current on cylinders of egg white. 



Mast (1931b) repeated and extended Kiihne's experiments and ob- 

 tained results which confirm his contentions. It may then be assumed with 

 considerable confidence that when an amoeba is subjected to a direct 

 current, the hydrogen-ion concentration in the cytoplasm decreases at 

 the cathodal end and increases at the anodal end. 



Edwards (1923) demonstrated that if an alkaline solution is locally 

 applied to the surface of an amoeba, the plasmagel in this region dis- 

 integrates; and that if acid is applied, it becomes thicker, owing to gela- 

 tion of the adjoining plasmasol. This has been confirmed indirectly by 

 Pantin (1923), Chambers and Reznikoff (1926), and others. If, then, 

 the direct current produces a decrease in hydrogen-ion concentration at 

 the cathodal end and an increase at the anodal end, one would expect 

 the plasmagel to become thinner at the cathodal end and thicker at the 

 anodal end. This is precisely what was observed. And if the elastic 



