324 MOTOR RESPONSES 



in different current densities, extending over a wide range. He maintains 

 that the results indicate that i\/t — a) = K. This equation is similar 

 to the one obtained by Kamada in observations on the destruction of the 

 surface membrane in paramecia by a direct current. It is also related to 

 the one obtained by Hahnert (see above) in his observations on the 

 cessation of streaming in Amoeba in a constant current. 



Internal processes involved in response. — Several theories have been 

 formulated to account for the responses of ciliates to an electric current. 

 Loeb and Budgett (1897) contend that these are in reality the result of 

 responses to changes in the chemical constitution of the environment 

 produced by the electric current. Pearl (1901) asserts that the direction 

 of the stroke of the cilia is specifically correlated with the direction of 

 protoplasmic streaming directly below the surface. Coehn and Barratt 



(1905) hold that the movements are purely cataphoretic; Bancroft 



(1906) maintains that the galvanic responses are due to local changes 

 in the calcium content of the tissue in relation to that of other ions, 

 especially monovalent cations. Although Carlgren (1899) lays especial 

 stress on localized changes in water content within the organisms, due 

 to endosmotic streaming. Some assert that the movements are due to 

 direct action of the electric current on the cilia, others that they must 

 be due to action on a coordinating center. Ludloff (1895), Verworn 

 (1895 ) , and Koehler ( 1925 ) postulate functional division of the organ- 

 isms into anterior and posterior halves, such that one responds in one 

 way that the other responds in another way. The views of Nernst ( 1899) , 

 Lucas (1910), Lillie (1923), and others regarding stimulation in higher 

 organisms would lead to the idea that local changes in permeability of 

 the surface membrane is the all-essential in controlling the movements 

 of the lower organisms in an electric field. 



The relation between these hypotheses and the facts established has 

 been very illuminatingly discussed by Jennings (I906) and Koehler 

 (1925). Both conclude that the facts in hand are not adequately ac- 

 counted for by any of the hypotheses presented. Jennings contends, as 

 previously stated, that the most important perceptible characteristic of 

 the response is reversal in the direction of the stroke of the cilia on the 

 cathodal side. Koehler holds that the processes involved cannot be solely 

 dependent upon surface phenomena, that somehow the current results 

 in a division of the organism into cathodal and anodal portions which 



