THE PROBLEM OF NEURON PATTERN 175 



applicability. For example, the localization of the axon 

 outgrowth is regarded as corresponding to the "anodic 

 extension" observed by Verworn and others in Protozoa 

 and certain other forms exposed to an electric current. 

 Assuming that this anodic extension possesses a greater 

 permeability for negative than for positive ions and 

 referring to the evidence indicating that the medium 

 about the neuroblast contains a considerable amount of 

 potassium salts, Kappers maintains that the anodic 

 extension will take up more negative ions than other 

 parts of the cell and also more negative than positive 

 ions and so will become electronegative and therefore 

 positively anodotactic, i.e., it will be attracted by the 

 anode and grow toward it. 



The localization and outgrowth of the chief dendrites 

 toward the cathode are regarded by Kappers as repre- 

 senting the normal or usual cathodotaxis. The dendrites 

 grow out only after the cell contains Nissl granules, which 

 are also present in the dendrites. These granules are 

 supposedly of nuclear origin and therefore acid and 

 electropositive, according to Kappers. He also suggests 

 that the cataphoresis of albumens may play a part in 

 the localization and direction of the outgrowths. Alka- 

 line albumen particles move toward the anode and acid 

 albumens toward the cathode of a current passing 

 through the medium in which they are suspended. A 

 more extended consideration of these and other special 

 assumptions which Kappers makes to account for the 

 facts is impossible and, I believe, unnecessary here, for 

 I shall endeavor to show that they are not essential to 

 an interpretation of the developmental processes con- 

 cerned in terms of reaction to an electric current. 



