130 Experiments on the Development of Peripheral Nerves 
important additional evidence for this view, the conclusion of Braus,” 
who was the first to experiment upon this phase of the question of nerve 
development, are diametrically opposed to it. Braus interprets his results 
in accordance with Hensen’s hypothesis. While one cannot but admire 
his ingenuity of experimentation and argument, his results are not, in 
my opinion, in any way inconsistent with the outgrowth theory. The 
growth of strange (facial or pelvic) nerves into a transplanted fore limb 
can be accounted for on the assumption, for which there is good evidence, 
that the configuration of the various organs and tissues plays an impor- 
tant part in determining the course taken by growing nerve fibers. The 
failure of the nerves of the host to grow into “ aneurogenic ” buds, while 
they do grow into “ euneurogenic ” transplantations, might be due to the 
absence of the attraction afforded in the latter by the cut ends of the 
nerves.” The large size of the nerves in the transplanted limb as com- 
pared with the nerves connecting them with the center, may be due 
partially to the presence of the sheath cells transplanted with the bud, and 
partially to an abnormal number of dividing fibers. Braus does not ex- 
clude beyond doubt the possibility of the latter. In any case the evidence 
for autogeneration of fibers could be regarded as crucial only if nerves 
having no nervous connection whatever with the center are developed in 
the transplanted part. This condition Braus has failed to demonstrate. 
While the facts necessitate our deciding against the validity of Hensen’s 
view, as far as the question of primary continuity is concerned, it should 
be pointed out before closing that this view is in so far correct as in many 
instances the nervous connection between center and end organs is estab- 
lished when the two are very close together, and the long nerve paths origi- 
nate in such cases by the moving apart of center and innervated organ 
after the establishment of the connection. The best example of this is seen 
in the lateral line. Here the ganglion is practically in contact with the 
rudiment of the sense organs when the first nerves are developed. The 
cell processes have merely to grow out for a distance less than the diam- 
eter of a cell in order to make connection. Yet by the wandering of the 
sensory epithelium from the head to the tip of the tail the lateral branch 
5’ W. H. Lewis, Proceedings Ass. Am. Anatomists. Am. Journ. of Anat., 
Vol. V, No. 2, 1906. 
°H. Braus, Verhandl. d. Anatom. Gesell., Jena, 1904. Anatom. Anz., Bd. 
XXVI, 1905. 
1% Forssman (Ziegler’s Beitrage, Bd. 24, 1898, and Bd. 27, 1900), has shown 
beyond question that a tropism of this kind does play an important part in the 
regeneration of peripheral nerves. 
