DEGENERATION AND REGENERATION OF NERVE FIBERS 491 
Howell and Huber (’92) also saw and described these proto- 
plasmic bands, and, while they were unable to confirm Biingner’s 
observations on the differentiation of axons in them, they re- 
garded them as ‘embryonic nerve fibers’ capable of receiving and 
conducting impulses. In case of a failure of the two ends of 
the nerve to unite, regeneration stopped with the formation of 
the protoplasmic bands. In case of union of the two stumps, 
the bands of the peripheral stump fused with those of the cen- 
tral stump; next myelin sheaths were laid down within the bands 
and new axons grew down into them from the central stump. 
Stroebe (93), using his now well known stain, was able to 
demonstrate the outgrowth of new axons from the central end, 
but thought that the myelin sheath was formed as a continua- 
tion of the old sheath and accompanied the axon in its forward 
growth. He was unable to demonstrate any connection be- 
tween these new fibers and the protoplasmic bands seen by 
Biungner in the peripheral stump. 
Working with Stroebe’s method, Huber (’95) was able to 
secure much clearer pictures of the regenerating nerve fibers 
than had been seen before, and showed that the axons grew out 
from those of the central stump and, in some cases at least, en- 
tered the substance of the protoplasmic bands of the peripheral 
stump. He was able to see some which ended abruptly in the 
protoplasm of the bands, their free ends directed toward the 
periphery and occasionally presenting bulbous enlargements. 
Ziegler (96) ascribed the origin of the new axons to the neuri- 
lemma, cells of the central stump and thought that at the time 
of their first appearance they had no connection with the old 
axons. Galeotti and Levi (95), Kennedy (’97), and Wieting 
(98) thought that the new axons developed in situ in the periph- 
eral stump. It is clear, therefore, that even before Bethe began 
his work the opinions of those who had worked at the question 
from the histological side were about evenly divided. This 
shows that the histological methods at their disposal were not 
adequate for the solution of the problem. 
Since investigators had failed to show conclusively the nature 
of the regenerative processes:when the two stumps had been 
