310 



MOTOR RESPONSES 



opposite end decreases in size, breaks up, and becomes yellow just as do 

 amoebae killed in an acid solution, and the granules in the amoeba then 

 move toward the anode, all indicate ( 1 ) that the granules bear a negative 

 charge, ( 2 ) that water in the amoeba is carried toward the cathode, and 

 (3) that the plasmagel at the anodal surface becomes acid. 



In very accurately controlled observations on A. proteus, in direct 

 current, Hahnert (1932) found that there is at first a momentary in- 

 crease in rate of locomotion and then a gradual decrease. He also noted 



Figure 113. Graphs showing comparative effect of different densities of current on the 

 rate of locomotion. Abscissae, time in minutes, (A) before and (B) during the passage 

 of current; ordinates, apparent rate of locomotion. To obtain actual rate in millimeters 

 per minute, divide the apparent rate by 85. (After Hahnert, 1932.) 



that the rate of decrease varies directly with the current density (Fig. 

 113), and that the time required to induce cessation of movement in 

 specimens directed toward the anode varies nearly inversely with the 

 square of the current density, "the time-intensity relation being nearly 

 in accord with the equation /^// — (xi) = K in which / is the intensity 

 of the current and / its duration." 



Alternating current. — If an active Amoeba mounted in culture fluid is 

 subjected to a weak alternating current, locomotion ceases at once. The 

 pseudopods are then retracted partially or entirely, and the animal be- 



