NEUROBIOTAXIS 279 
The outgrowth of the axis-cylinder begins in the chick embryo 
about the second day of incubation (Bok). 
Not until much later—according to Cajal when the growth 
tip of the axis-cylinder has reached, or nearly reached, its end 
point (about the 6th day of incubation in the chick embryo, 
Bok)—does an outgrowth of the dendrites begin, which make 
their way in the direction of the stimulus, that is in the direction 
of the kathode. 
THE FORMATION AND CONTRACTION OF DENDRITES. THE FINAL 
SHIFTING OF THE PERIKARYON 
I believe that there is a principal difference biologically as well 
as biochemically between the anode elongation of the axon 
and the kathodic tropism of the dendrites. 
The primary growth of the axon is in the beginning not di- 
rected to a certain point, but merely from a certain kathodic 
center, the outgrowth of dendrites, however, is much more 
influenced also in the beginning by their final end-points. 
Their tropism corresponds with the regular appearance of the 
law of stimulation of protoplasm and exhibits a kathodic char- 
acter, probably related with a more advanced nervous function 
for which a further stage of development is necessary. 
This kathodic growth direction, as well as the kathodic taxis, 
is the usual thing in nature and, as Loeb and Maxwell have 
shown, is in harmony with Pfliiger’s law. We only have to 
prove that there are no factors which might interfere with it 
and change it into an anodal elongation. 
This question is the more important since it may be that in 
the first phase of outgrowth of dendrites, which is not yet ac- 
companied by a secondary shortening of the dendrite and the 
shifting of the perikaryon, a kataphoretic process might intro- 
duce it or at least be involved in it. Anyhow, the kataphoretic 
qualities of the dendrites may never be such that they should 
counteract the kathodo-tropic process which certainly is the 
chief factor in the shortening (contraction) of the dendrite and 
the shifting of the cell. 
