320 MOTOR RESPONSES 



they are carried. They contend that the contact of these granules with 

 the inner surface of the plasmagel causes it to hquefy, and that this 

 results in the formation of a pseudopod which is directed toward the 

 cathode if the granules are positively charged and toward the anode if 

 they are negatively charged. These authors say: 



As the granules move either toward cathode or anode, they must tend to 

 break down the thixotropic gel on the side toward which they move. . . . 

 If this gel is liquefied in any local region, such a region becomes pushed 

 out to form an advancing pseudopod. 



These are interesting views, but they obviously do not account for 

 the direction of movement of pseudopods in alternating current (Fig. 

 114), nor for the direction of movement of pseudopods under some 

 conditions in direct current (Fig. 112). For this would require cata- 

 phoretic movement of the granules perpendicularly to the direction of 

 the current in the former, and in opposite directions at opposite ends 

 of the amoeba in the latter. Moreover, the fact that the granules stream 

 toward the anode after the amoeba disintegrates, indicates that they are 

 normally negatively (not positively) charged, and that this charge is 

 consequently not involved in the cathopositive response. How, then, can 

 the observed reversal in the direction of orientation be explained? 



The cathopositive response is probably brought about as described 

 above. The ammonium hydrate or chloride added to the culture fluid 

 probably results in the liquefaction of all the plasmagel, and conse- 

 quently in free movement toward the anode of the negatively charged 

 granules suspended in it. According to this view, the reversal in the 

 direction of galvanic orientation is due to liquefaction of the plasmagel 

 caused by the ammonium compounds used, not to change in the electric 

 charge on the "protoplasmic granules." 



B. FLAGELLATES 



Some of the flagellates orient very precisely in a direct current. Some 

 are cathopositive, others anopositive, and still others both or neutral, 

 depending upon the environmental conditions (Verworn, 1889; Pearl, 

 1900; Bancroft, 1913). Verworn maintains that orientation is brought 

 about by differences in the effective stroke of the flagellum in opposite 

 directions. Pearl believes that it is the result of typical avoiding reac- 



