96 
ZOOLOGY: S. R. DETWILER 
Proc. N. a. S. 
ON THE HYPERPLASIA OF NERVE CENTERS RESULTING 
FROM EXCESSIVE PERIPHERAL LOADING 
By S. R. Dejtwiler 
OSBORN ZOOLOGICAI. LABORATORY AND THE ANATOMICAL LABORATORY, YaI,E UNIVERSITY 
Communicated by R. G. Harrison. Read before the Academy, November 10, 1919 
A number of investigators (Braus,^ Shorey,^ Diirken,^ and Burr^) 
have shov^n that the destruction of peripheral areas in the embryo may 
result in an incomplete development (hypoplasia) of the nerve centers, 
either encephalic or spinal, which normally supply the peripheral area 
with nerves — the defective development resulting, supposedly, from a 
lack of functional demands which are ordinarily imposed upon the develop- 
ing nerve centers. Particularly has this been observed in connection with 
experiments on the development of amphibian limbs. 
The cumulative evidence favors the idea that complete development 
of the nerve centers will not take place unless under the influence of the 
functional activity of the end organ. The extent, however, to which 
function may effect development is a question concerning which the re- 
sults of investigators stand at variance. Moreover, no experiments have 
hitherto been carried out to show whether, by increasing the functional 
demands at the periphery, it is possible to effect a corresponding increased 
development (hyperplasia) of the nerve centers. & i f-; « ^ 
The experiments reported in this paper have shown that by effecting an 
increase in the peripheral area it was possible to bring about a hyperplasia 
of the sensory nerve centers. The experiments which have disclosed this 
fact consisted in transplanting the right anterior limb rudiment of Ambly- 
stoma punctatum a given number of body segments posterior to the normal 
position, whereby it was possible to study the effects of the continued 
function of limbs so placed upon the development of the sensory and motor 
nerve centers in that region of the cord supplying the limb with nerves. 
A brief account of the innervation and the function of limbs so transplanted 
has previously been published (Detwiler^) . 
Limbs transplanted the distance of more than three segments posterior 
to the normal position receive the bulk of their nerve supply from seg- 
ments of the cord just posterior to the normal limb level. An examination 
of the peripheral nerves of this level shows that those contributing fibers 
to the functioning transplanted limbs are larger than their counterparts 
which are not connected with a limb. 
In an endeavor to show whether this increase in the number of periph- 
eral neurones was due to a hyperplasia of the motor centers, attempts 
were made to compare the number of motor nerve cell bodies in both halves 
of the spinal cord at the level in question. The larvae having been pre- 
served at a relatively young stage (sixty to seventy days after the closure 
of the medullary folds), it was impossible to differentiate accurately be- 
