NEUROBIOTAXIS 269 
the shifting of the cell body, both of which also only occur later 
and which move towards the center, 1.e., poe the current of 
the stimulus that proceeds to them. 
This observation and Bok’s interpretation of it are very 1m- 
portant, and no doubt correct. It is evident, however, that the 
final end-point of the growing axis-cylinder can not be deter- 
mined by this process alone, as was also realised by Bok, who 
came to the conclusion that the final connection was deter- 
mined by the principal law of neurobiotaxis, viz., by the stimu- 
lative (simultaneous) correlation of the growing axis-cylinder 
and its end-point, i.e., the cell or dendrites with which it is 
going to be connected. 
Bok thought that this could be effected by the fact that if 
two centers are in simultaneous stimulation the ideal line be- 
tween the two is the path where the plasmodesms undergo the 
greatest influence of this relation. He called this the principle 
of the ‘doppelte Bahnung,’ and thought that Einstein’s (physi- 
cal) law of attraction between synchronic energies also had some 
influence on it. 
It seems to me, however, that the principle of ‘doppelte Bahn- 
ung,’ as laid down in this theory, can not explain from which of 
two simultaneously stimulated cells the axis-cylinders grow out, 
and that,even the adaptation of the protoplasm to the forma- 
tion of the axis-cylinder, eventually a fibrillation of the neuro- 
desms, then might begin in the middle between two cells which, 
as we know, it never does. Moreover, the expression “‘adapta- 
tion of protoplasm to its biological function” is too general an 
expression to explain anything. 
It has appeared to me that the literature of recent years con- 
cerning the microchemistry of the neurones and the phenomena 
of tropism and taxis known and experimentally examined in 
other organisms, together with Bok’s discovery, concerning the 
14 Tf the normal stimulation of the cell body is of little importance or eventually 
absent, the cell may also shift in the same direction in which the axon grows out. 
(See my paper on the autonomic nervous system. Journal of Physiology, 1908, 
vol. 37, p. 139.) 
