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 
