Influence of the Nervous System 663 
It might even*be maintained from a study of the changes in 
ordinary amputated limbs only, that nerve impulses are not needed 
in the replacement of lost parts; for it was found that after amputa- 
tion the severed nerves broke down near the cut end and continued 
to degenerate proximally; and that while these processes were 
going on, the bone proliferated cartilage, the old muscles regener- 
ated new ones, etc.; and that only after the new leg had grown to a 
considerable size did the nerves grow into them. If the conclu- 
sion were based on this evidence of ordinary regeneration alone, 
it might be claimed that the facts did not show whether an 
initial stimulus—before the degeneration of the nerves had begun— 
may not have sufhiced to start the regenerative processes. This 
criticism has, however, been thoroughly offset: in the experiments of 
the previous sections on paralyzed and partially paralyzed animals. 
Dorsal Ganglia of Plexus Destroyed 
Up to this point the removal of motor impulses alone was con- - 
sidered. Much time was given to this problem, because accord- 
ing to prevailing opinion the “morphogenic” and “trophic” 
influences travel or originate in the motor system. Herbst and 
others, however, believe that sensory stimuli exercise a controlling 
influence in regeneration. In this section we will examine the 
effect of removal of either the dorsal ganglia alone or the dorsal 
ganglia and the nerve cord. 
While the cord may be readily removed, the destruction of the 
dorsal ganglia is not a simple matter. Each ganglion is encased 
in a bony compartment. Attempts to remove the ganglia by 
cutting out the spinal column led to the death of the individuals. 
The method finally adopted was to open one side (the left) of the 
anzesthetized animal in the region of the pelvis, expose the nerves 
that innervate the limb, trace them as near as possible to their 
origin and after destroying the protecting bone with a broach or 
hot needle, scrape the contents most thoroughly. ‘The slit was 
then sewed and both legs amputated. ‘The cord was destroyed in 
many animals either by breaking through the sides of the neural 
arches or, as in previous sections, by piercing the vertebral canal 
by way of the tail. 
