741 
deviations were greater in proportion as the operative trauma for 
the investigation had been larger. Moreover they found a permanent 
regularity in the way in which the deviations presented themselves. 
These facts brought them to the view that the isolated root-field 
that could experimentally be ascertained, can never have the entire 
extent of the theoretical dermatome. They supposed therefore that 
even in the most favourable experiments beyond the limits of the | 
sensible zone, always another little strip of skin must be admitted 
as belonging to the dermatome. This strip they called “Marginal area”, 
and pronounced ia. the hypothesis which for the rest was no further 
elaborated, that this strip is not capable of independent sensation (i.e. 
without the assistance of the overlapping). This isolated sensible zone 
they called “central area”. In the experiments of W. and v. R. tue 
form and extent of this zone appeared to be extremely variable and 
dependent on the postoperatory conditions of the isolated root and 
of the spinal cord. With a large operative trauma the form of the 
central area was no more than a ‘caricature’ and its extent much 
smaller than might be expected from the dermatome. W. and y. R. 
call this part of the dermatome, that was found to be insensible 
likewise ‘marginal area”. If we summarize W. and v. R.’s views, we 
find that even in the most favourable experimental isolations the 
zone that is found to be sensible does not constitute the whole theo- 
retical dermatome, but only a central area of it shut in between two 
marginal zones that cannot be indicated. In unfavourable cases, when 
the central area becomes a caricature, the marginal area is widened 
at the expense of the central area. 
In W. and v. R.’s experiments the latter phenomenon always 
occurred first and strongest in the ventral zone of the dermatome. 
As an explanation of the fact that the sensibility in the ventral zone 
appears to be feebler W. and v. R. adduce two hypotheses : 1st that 
the ventral part is the most excentric part of the dermatome (i.e. 
most distant from the C.Z.S: spinal cord and spinalganglion) ') and 
2ad that on account of the “stretching” of the skin between manu- 
brium sterni and symphysis the extremities of the nerves had to 
extend over a larger surface than in the dorsal zone. 
On the occasion of a systematic examination of the strychnine- 
1) Compare likewise: G. VAN RIJNBERK. On the fact of sensible skin dying away 
in a centripetal direction Proc. of the K. Akademie v. Wetenschappen te Amster- 
dam 1903, and G. van RinBerK. Beobachtungen über die Pigmentation der Haut 
bei Seyllium catulus und canicula und deren Zuordnung zu der segmentalen Haut- 
innervation dieser Thiere. Petrus CAMPER. Nederl. Bijdragen tot de Anatomie. 
Di. Ill. p. 137. Haarlem. 1904. 
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