1145 
the covering would likewise be demonstrated experimentally. This 
bowever has only value as a theoretical method and could not 
experimentally be applied. For the action-currents flowing from one 
spot of the skin to the central nervous-system are certainly much 
too weak to be conducted to the string galvanometer. 
I have however obviously proved by a circuitous way in my 
experiments described above, that after irritation of one part of the 
skin, action-currents must flow from each part of the skin to the 
central nervous-system at least along two hind roots. For if I have 
determined with the eat of Fig. 1 the root-field of thoracalis IX, 
the hyperreflectory field disappears, after the hind-root of thoracalis 
IX has been cut. If then I moisten the spinal cord behind hind-root 
X part of the root-field of thoracalis LX becomes again hyperreflectory 
(this part has been hatched in the figure). Consequently action-currents 
will flow to the central nervous system from this hatehed skin-field 
both along the hind-root of thoracalis IX and that of thoracalis X. 
If we isolate a dermatome by cutting on either side two or three 
hind-roots, how is then the division of the separate radicularia of 
which each hind-root consists over the dermatome belonging to it. 
WiNkKrER and vaN RIJNBERK found with regard to the hind-roots, 
that, if one bundle had remained intact, the sensibility continued 
over a field, that as to form and extent could not be distinguished 
from the field that had been found after isolation of the entire root. 
Dusser DE BARENNE moistened the spot of entrance of two fila radicu- 
laria of one dorsal root with a solution of strychnine (1°/,) and 
obtained then the complete strychnine-dermatome. 
I have studied this problem again for the strychnine-dermatomes. 
If we try to solve this question, we must direct our investigations 
to root-fields that appear in their full extent, and in the second 
place we must be sure that the stimulant applied can be applied 
strictly locally. The strychnine-isolation can satisfy these two demands 
as much as possible. I proceeded hereby first in a different way from 
that of Dusskr De BARENNE and arranged my investigations into this 
subject in the following manner: After | had laid bare the spinal- 
cord for a sufficient length and opened the dura, I cut cranially and 
caudally from one hind-root two or three hind-roots. Then I deter. 
mined according to the strychnine-method the root-field of the isolated 
root. When I had then obtained a sharply limited field, J cut at the 
anterior or the posterior side of this hind-root either some radicularia 
or all but one or two. The result was then such, that a strip of the 
74 
Proceedings Royal Acad. Amsterdam. Vol. XVIII. 
