120 Ss. R. DETWILER 
The method of attacking this problem up to the present time 
has consisted in extirpating the end organ at a period either 
before or shortly after the peripheral nerves have begun to de- 
velop and of observing the effect of its absence on that part of 
the central nervous system ordinarily supplying it with nerve 
components. 
Braus (’06) extirpated the forelimb buds of Bombinator at a 
period prior to the outgrowth of the brachial plexus, with a view 
of determining the effect of the absence of the limb on the ventral 
horn region of the spinal cord corresponding to the limb level. 
It was found, from a study of larvae preserved ten days after 
the operation, that the brachial nerves had grown out to the 
limbless area and that they were as well formed as those onthe 
uninjured side. No reduction in size or number of the ventral 
horn cells could be detected. Observations, however, on operated 
larvae which were kept alive until just before metamorphosis 
showed that not only was the brachial plexus on the limbless 
side diminished in size when compared with its counterpart, but 
that, in addition, there was a distinct reduction in the size of 
the ventral horn area ordinarily supplying the limb. Asa corol- 
lary to the general developmental theory of Roux (’85), Braus 
concluded that the development of the ‘central nervous system,’ 
is readily divisible into two periods: the first, in which growth 
and differentiation are independent of functional activity, and, 
the second, in which further differentiation and growth continue 
only when under the influence of functional activity. 
Miss Shorey (’09), who performed a series of extirpation ex- 
periments on the limb buds of the chick and the amphibian 
embryos, came to the rather sweeping conclusion from her find- 
ings that no neuroblasts are self-differentiating and that all are 
alike dependent for differentiation on stimulation from end 
organs or from the products of the activities of end organs. 
Although the experiments of Harrison (10) left no doubt that 
the initial differentiation of the nerve fiber is a factor predeter- 
mined within the neuroblasts, they did not attempt to give any 
definite information on the part played by functional activity on 
the later differentiation of neuroblasts. 
