174 THE ORIGIN OF THE NERVOUS SYSTEM 



toward the anode, the dendrites arising on the side 

 toward the negative pole or cathode and growing toward 

 the cathode of this field. Kappers accounts for the pres- 

 ence of the electrical field by the fact that a region of ex- 

 citation becomes electronegative to its surroundings, and 

 assumes that the electrical field to which the neuroblast 

 reacts results from the stimulation of a neuron or group 

 of neurons or axons in the vicinity of the neuroblast in 

 question. The neuroblast itself he regards as sur- 

 rounded by a fluid medium, the lymph, containing 

 electrolytes and therefore conducting the current. 

 According to the hypothesis, the neuroblast reacts to 

 this electric current by localization and growth of axon 

 and chief dendrite at opposite poles of the cell and later 

 by shifting of the cell body toward the negative pole or 

 cathode. The growth of the axon is then "stimuli- 

 fugal," that of the dendrite "stimuli-petal." 



As various authors have shown, the usual galvano- 

 tactic response of living organisms is toward the cathode, 

 though this reaction may be reversed in many cases by 

 changes in the surrounding medium, such as increase in 

 concentration of electrolytes. If, however, the polarity 

 of the neuron is a galvanotactic response of the sort 

 Kappers postulates, it shows both positive cathodotaxis 

 and positive anodotaxis. In order to account for this 

 opposite reaction of axon and dendrites and for various 

 other facts, such as the usual condition with one axon 

 and several or many dendrites, the appearance of the 

 axon earlier than the dendrites, etc., Kappers is forced 

 to make a number of special assumptions, all of which 

 have a physicochemical basis, but which seem to me 

 greatly to complicate the hypothesis and limit its 



