NEUROBIOTAXIS Bae 
non of kataphoresis. I refer here to the investigations of 
Hardy,?8 which showed that as long as an albuminous solution is 
alkaline the particles suspended in it shift towards the anode 
on the transmission of a constant current, whereas they shift 
towards the kathode when the solution is made slightly acid. 
One is apt to look for an explanation of this also in the fact 
that on the boundary between a colloid particle and the sur- 
rounding fluid, a double layer in the sense of the theory of Helm- 
holtz-Quinke is present. 
If now the solution is alkaline, a transmission of ions will 
take place, in consequence of which the albuminous particle 
itself becomes negative and thus shifts to the anode on the 
transmission of a constant current, while in the case of an acid 
reaction of the surrounding “fluid the contrary takes place. 
From the reversibility of the kataphoretic phenomenon (Ham- 
burger)?’ the curious fact thus follows, viz., that also proteid 
particles have the peculiarity that their electric character is 
determined by the reaction of the surrounding medium. 
That here too, just as in the above tropism of the root-tips, 
an iso-electric condition occurs is clear. 
APPLICATION OF THESE EXPERIMENTS TO THE GROWTH OF THE 
NEUROBLAST. THE FORMATION OF THE AXON 
If, with these facts before us, we consider the phenomena 
which appear during the formation of an axis-cylinder*®® in an 
activated cell (which precedes the formation of dendrites—see 
*8 Hardy. On the coagulation of proteid by electricity. Jour. of Physiol., 
vol. 24, p. 2881, 1899. Proc. Roy. Soc., vol. 68, p. 110, 1900. 
29 Hamburger. Osmotischer Druck und Ionenlehre. Wiesbaden, Bergmann, 
1904, vol. 3, p. 68. ; 
30 Tt is hardly necessary to say that the fact that isolated ganglion cells, as in 
Harrison’s experiments, may also send out axis-cylinders proves nothing against 
the following text. Harrison (loc. cit., p. 833) remarks that this is a process of 
self-differentiation entirely independent of external conditions. This is true to 
a certain extent, but we must assume that before it becomes a self-differentiation 
its differentiation has been induced to the neuroblast in former generations by 
external circumstances and that its doing this by itself is based on hereditary 
engrammatic qualities. It is better to see a problem in things than to explain 
them by a word which implies a still greater problem. 
