MOTOR RESPONSES 333 



Responses to Chemicals 

 a. rhizopods 



None of the rhizopods except Aiiweha has been studied with refer- 

 ence to motor responses to chemicals. Many of the observations made 

 on Amoeba are so indefinite that further work under more carefully con- 

 trolled conditions is highly desirable. In this work the large form, 

 Pelomyxa carolinensis, which can now be readily procured, would doubt- 

 less be very favorable. 



Using a capillary pipette, Edwards (1923) applied various chemicals 

 locally to the surface of active specimens of A. proteus. With a few of 

 these chemicals he obtained fairly definite results, which lead to the 

 following conclusions: 



If an alkali comes in contact with the side of an active amoeba, stream- 

 ing stops and a local protuberance is formed at the point of contact. If 

 the solution is weak, the protuberance develops into a normal pseudopod, 

 which continues indefinitely toward the source of the solution. If it is 

 strong, the protuberance breaks at the tip and the central portion of the 

 amoeba flows out, leaving nothing but a crumpled membrane. 



If an acid is applied, streaming stops and a similar protuberance is 

 formed but it does not become large and does not develop into a nor- 

 mal pseudopod. If the acid is weak, the streaming soon begins again 

 and the protuberance gradually disappears. If it is strong, the protuber- 

 ance is very small and pseudopods form on the region opposite the point 

 of application. 



If acid is applied after a rupture in the surface of an amoeba has been 

 produced by local application of an alkali and after the central portion 

 begins to flow out, the flow immediately stops and the amoeba soon 

 proceeds normally. These and other facts show that alkalies cause the 

 cytoplasm of Amoeba to solate and that strong acids cause it to gelate; 

 but what is involved in the formation of a protuberance by weak acid 

 at the region of application is not clear. 



A strong solution of sodium chloride results in formation of pseudo- 

 pods opposite the region of application; a weak solution results only in 

 the formation of a protuberance in the region to which it is applied. 

 Thus Amoeba is negative to a solution of this salt if it is strong, and 

 positive if it is weak. This indicates that the former induces gelation of 



