THE PROBLEM OF NEURON PATTERN 177 



difficulties, some of which may be briefly pointed out. 

 In the first place, this hypothesis does not account for 

 the outgrowth and orientation of axons and dendrites 

 of the neuroblasts which first undergo differentiation in 

 the nervous system, for it assumes the presence of 

 functional neurons as the source of the current. Second, 

 Rappers assumes that the neuroblast is more or less 

 completely suspended in a fluid medium, consisting of 

 lymph, containing electrolytes, while, as a matter of 

 fact, it is in its earlier stages part of a very compact 

 tissue, which may be more or less syncytial in character. 

 At any rate, the cells are apparently in close contact, 

 and tissue continuity exists to a high degree. Later in 

 development of course the neurons do become more or 

 less separated by the substance of the neuroglia, by 

 lymph spaces, and probably by colloid gels, but differ- 

 entiation begins long before these changes have occurred. 

 Third, the hypothesis does not take into account in any 

 way the metabolic activity concerned in the localization 

 and outgrowth of axon and dendrites, but this is con- 

 ceived as almost entirely a matter of electrical attraction 

 between bodies of opposite sign. Actually, however, 

 these processes involve localized metabolic activity, 

 including oxidation and synthesis of new protoplasmic 

 substance. Moreover, if positive cathodotaxis, such as 

 Kappers assumes to underlie the outgrowth of the 

 dendrites, is associated with cathodic stimulation, as 

 many facts indicate, we should expect the side of the 

 neuroblast toward the cathode to be more active than 

 the other, and the dendrites should arise before the 

 axon, but the reverse is the case. Fourth, the "anodic 

 extension" observed by Verworn in certain forms in the 



