DEGENERATION AND REGENERATION OF NERVE FIBERS 505 
times appears distinctly striated, as is shown in the drawing 
at one end of the band. Such a longitudinal striation has lead 
Bingner, Bethe, and others to suppose that they had before 
them the beginnings of a new axon. Even Marinesco (’05) 
using Cajal’s method was at first led into this error; but later, 
perhaps with better preparations, he changed his view and 
adopted the conception of the outgrowth of the axon from the 
central stump. There are absolutely no transition stages between 
such striations and the new axons, which, when they first appear 
in the peripheral stump, are sharply defined from all surrounding 
structures (fig. 28). Even at this stage, nineteen days after 
the operation, these protoplasmic bands are capable of serving 
as paths for the developing axons. A considerable number of 
fine black fibers can be seen in the proximal part of this distal 
stump. They le in the protoplasmic bands and run around 
the droplets of myelin. These new axons can be followed by 
a study of the serial sections back to the scar through which 
they have traveled from the central stump. 
In Dog x, in which 1 cm. of the nerve was excised, a careful 
study of serial sections fails to show any axons which have 
pierced the intervening scar and entered the distalstump. In 
these preparations, therefore, we are able to study the proto- 
plasmic bands without any complication from ingrowing axons. 
The length of time from operation to autopsy in this experi- 
ment was twenty-five days. Most of the detritus from the 
axons and myelin sheaths has been absorbed, but one sees scat- 
tered through the field a few good sized droplets. The proto- 
plasmic bands have assumed a fairly uniform contour and stain 
a light yellow. Fine black granules are scattered through the 
protoplasm. These are sometimes arranged in parallel rows, 
giving a striated appearance. In none of these fibers is there 
any indication of the beginning of an axon. This is significant 
when taken in connection with the preceding case in which the 
two stumps were united, and in which, although the time between 
operation and autopsy was six days shorter, new axons could 
be seen in many of the protoplasmic bands in the neighborhood 
of the sear. 
