NEUROBIOTAXIS 2ae 
This first outgrowth which, in the beginning, can be compli- 
cated with an anodal katophoretic shifting of the cell body itself 
(fig. 4) may be entirely independent of a propagation of the 
nervous current itself along the newly formed short axis-cylinder. 
As soon, however, as this axis-cylinder is fit for nervous conduc- 
tion its rate of outgrowth will be considerably increased, a 
much stronger negative current running in the direction of its 
growth to the anodal field. 
Why does this anodic growth occur before the kathodic trop- 
ism of the dendrites and the cell body? I will consider this 
question in the light of the above-mentioned experiences. 
We know that the neuroblast is embedded in an organic solu- 
tion, the pericellular lymph, containing a good deal of potassium 
salts. 
Macallum has emphasized that the amount of potassium salt 
external to the nerve cell is great and that a considerable con- 
densation of this element is present on its exterior surface. 
Now Verworn has shown that on the transmission of a constant 
current the first thing to appear is an anodal expansion oi the 
cell body, thus showing that a change of tension may be local- 
ised, by electric influences, on the anodal pole. 
We may expect that this extension, being under the influence 
of a considerable amount of K and Cl, derives certain chemical 
and tropic characteristics from it. 
That this really occurs in nerve cells is proved by the chemi- 
cal constituents of the axon, compared with those of the den- 
drites and cell body. 
We know from the researches of Macdonald, Macallum, Al- 
cock and Lynch that the axis-cylinder is distinguished from the 
dendrites and the cell body by a much larger quantity of po- 
tassi1um and chlorides*® (which, according to Macdonald, may 
also contribute to its conductivity for the nervous current). 
32 MacDonald. The injury current of nerves, The key to its physical struc- 
ture. Report of Thomson-Yates Laboratory, vol. 4, 1902, p. 213. 
MacDonald. The structure and function of nerve-fibers. Proceedings of the 
Royal Society, vol. 76, B. 1905, p. 322. 
Macallum. On the distribution of potassium in animal and vegetable cells. 
Journal of Physiology, vol. 32, 1905. 
Macallum. Die Methoden und Ergebnisse der Mikrochemie in der Biologis- 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, NO. 3 
