276 Cc. U. ARIENS KAPPERS 
fig. 4), we shall first have to mention the fact that the stimula- 
tion center with respect to the surrounding tissue is negative, 
forming a kathode with reference to the non-stimulated sur- 
roundings, as physiological experiments abundantly prove. 
Moreover the strength of the electrolytic potential differences 
occurring in the nervous system in consequence of stimulation 
appears to be of the same category as those that are applied in 
artificial phenomena of galvano-taxis (see above) since it may 
vary from 3 millivolt to 0.8 millivolt and lower, so that the forces 
developed here are certainly strong enough to influence proc- 
esses of formative tropism and functional taxis. 
Now, it may be the same whether this stimulated center is 
the body surface in or under which nerve cells lie or whether we 
start our deductions with a primary growing axis-cylinder which 
on its way passes neuroblasts. This negative potential not only 
runs along the primary axis-cylinder (fig. 4) but also, we may 
assume, as long as the axis-cylinder is not provided with an 
insulating medullary sheath, that this negative potential stands 
perpendicular to the length of the activating axis-cylinder (or 
body surface), irradiating from it.*! 
In accordance with this perpendicular irradiation of the 
electrolyte nfluence, or current, we see that th neuroblasts 
near the primary activat ng bundle send out ax’s-cylinders per- 
pendicular to the activating bundle, and that similarly perpen- 
dicular collaterals may grow out from the original (activating) 
axis-cylinders themselves. 
In both cases, in the formation of collaterals as well as in the 
outgrowth of the axis-cylinder of the secondary (activated) 
neuroblasts, the axis-cylinder substance proceeds in the direc- 
tion of the perpendicular irradiation of the stimulated fiber, 
i.e., to the anodic pole. 
31 The irradiative stimulus of naked axons is very clearly illustrated by the 
position of the dendrites of Purkinje’s cells perpendicular upon the parallel 
fibers in the molecular layer of the cerebellum and of the dendrites of the motor 
cells on the longitudinal (naked) axons in the spinal cord of Petromyzon. See 
my paper, Ueber das Rindenproblem, etc., in the Folia Neurobiologica, Bd. 8, 
1914, pp. 529-530 
