Influence of the Nervous System 717 
These experiments together with those on earthworms and newts 
should make one cautious about accepting the view of the direct 
or even indirect influence of a nervous influence on regeneration. 
CONCLUSION 
Since summaries of each of the foregoing sections have already 
been given, I wish here only to emphasize certain essential points. 
No pains were spared to establish beyond dispute that the ner- 
vous system had been completely removed in those animals used 
to test this question. In no work heretofore published has this 
important consideration received sufficient attention. Wolff’s 
experiments most closely fulfill the conditions, yet in many of his 
animals the legs moved after three months, clearly indicating that 
all connections had not been destroyed or that new connections 
had been established. 
In the newt and in the earthworm at least, and very probably in 
the tadpole of the frog as well, all sources of nerve stimuli to the 
amputated region were destroyed. In these animals, the usual 
physiological tests to determine reflex action were supplemented by 
histological examination of the regenerated and adjacent regions. 
In this way the exact nature of the initial injury to the nerve cells 
and their fibers; and the consequent destructive and constructive 
changes of the nerve as well as the adjacent tissues were exactly 
determined in over one hundred different animals. 
In the hind leg of Diemyctylus for example, it was found that the 
nerve cord had been totally destroyed in the region of the lumbo- 
sacral plexus, in the tail and in one to six vertebre anterior to 
the plexus. ‘The destruction of the cord for so great a distance on 
either side of the plexus renders it certain that no motor stimuli 
could have reached the hind legs either from anterior or posterior 
levels. In many of these and in other animals, the sensory or 
spinal ganglia of the plexus and other nerves were also destroyed. 
Examination disclosed the fact that no subsequent regeneration of 
the nerve cord or ganglia or of the corresponding motor and sensory 
fibers took place within nine months after the operation. ‘The 
legs were completely paralyzed during the whole of this time. 
Despite the lack of allnerve connections, the typical structure of the 
leg, foot and toes were developed in every case. 
