DEGENERATION AND REGENERATION OF NERVE FIBERS 497 
of unknown extent at an unknown level and rendering difficult 
the accurate application of Langley and Anderson’s test of the 
presence of central connections by subsequent division of all 
nerves going to the leg. Positive results obtained by compli- 
cated and uncertain methods cannot outweigh the negative 
results obtained by simpler operative procedures. 
More recently Wilson (’09) has repeated some of Bethe’s 
work but came to no definite conclusions as to the nature of 
the processes involved in the regeneration of nerves. 
Space has not permitted a detailed report of all the work that 
has been done with the object of studying the changes which 
occur in a piece of nerve permanently cut off from the central 
nervous system; but enough has been given to show that this 
line of experimentation has, as yet, given no satisfactory evi- 
dence of the capacity of a stretch of nerve completely separated 
from the central nervous system to undergo an autogenous regen- 
eration. On the contrary, the more recent experiments of this 
sort show that so great is the regenerative capacity of the cen- 
tral stump in young animals that it is a matter of the greatest 
difficulty to exclude the possibility of axons from the central 
having reached the peripheral stump, and it is equally difficult 
to exclude the possibility of axons having grown into the periph- 
eral stump from other nerves in the vicinity. The only experi- 
ments that are entirely satisfactory are those of Lugaro, involv- 
ing the removal of the entire lumbo-sacral portion of the spinal 
cord and the associated spinal ganglia, and these experiments 
were negative. 
The reason that so many have attempted to solve the problem 
in this way is that no stain was available prior to 1903 which 
was capable of unraveling the complicated processes going on 
at the point of union of the cut ends of a divided nerve; and 
any attempt to determine what was going on in this zone with 
the use of any of the usual stains could searcely lead to con- 
vineing results. Under these circumstances it was but natural 
that an effort should be made to determine what happened 
under much simpler conditions in an isolated peripheral stump, 
not with the idea that any regeneration occurring here would 
