DEGENERATION AND REGENERATION OF NERVE FIBERS 533 
from a medullated fiber) containing five new axons, and at b 
a bundle of fine protoplasmic bands (formed from non-medul- 
lated fibers), in several of which new axons have appeared. 
All new axons lie in protoplasmic bands, never between them. 
It has been supposed by others that the axons may run between 
the bands as well as within them. This appears to be the case 
in longitudinal sections; but in cross sections one always sees 
the light yellow protoplasm of a band surrounding every axon. 
About some of these axons a faint halo of myelin is deposited 
by the thirty-fourth day. 
No cases were studied in which sufficient time had elapsed for 
the complete regeneration of the nerve. We expect to make 
other experiments on young dogs with a view to determining 
the structure of a fully regenerated nerve and especially the 
relative proportion of medullated and non-medullated axons 
which it contains. 
SUMMARY 
1. The idea, first clearly stated by Biingner, that the new 
axons arise in the protoplasmic bands through a fusion of longi- 
tudinal striations which have developed in situ, has been shown 
by the application of the Cajal stain to be without foundation. 
The axons, when they first make their appearance in the distal 
stump, are fully developed and clearly differentiated from the 
surrounding protoplasm. They do not appear as discontinuous 
fragments, but as long fibers, which, when traced peripherally, 
may either run out of the section or end within a protoplasmic 
band with a terminal bulb, and when traced centrally either 
run out of the section or into a plexus of axons in the scar. In 
these findings all recent investigations agree. Perroncito (’05), 
Marinesco (’06), Poscharissky (’07), and Cajal (08), who have 
used the Cajal stain, Pupura (’01) with Golgi stain, and Krassin 
(06) with methylene blue, have all reached the same conclu- 
sion. Their results are in full accord with those of the present 
investigation. Even Bethe (’07) is silent on the question of 
the histogenesis of the regenerated axons in the distal stump, 
since in his last article he makes no attempt to defend his for- 
mer views on this subject. 
