494 F. H. PIKE 
system by any remaining intact portion, declaring that it is not 
a useful conception in the explanation of the action of the nerv- 
ous system normally or of the processes occurring in its recovery 
from injury. 
If, by vicarious assumption, one means that some other cells 
and fibers which were never concerned directly or indirectly 
with the processes carried out by a second group when intact, 
assume a part of the function of the second group when the latter 
is injured, vicarious assumption becomes a mischievous as well 
as a useless hypothesis in the explanation of nervous processes. 
For, if one group of cells may take over a function with which it 
has had no previous connection, there is no localization of func- 
tion in the proper sense of the term. If such be its meaning, the 
term vicarious assumption of function should be dropped from 
neurology. 
The idea of compensation in the nervous system for injury 
to any of its parts should not, however, be disposed of so sum- 
marily. In order to show how such a compensation is susceptible 
of explanation in terms of nerve cells and fiber tracts without 
violating any of the postulates either of cerebral localization or of 
localization in the nervous system generally, I will ask leave to 
introduce here some conclusions to which I have been led from 
a study of certain processes of compensation for loss of partic- 
ular afferent channels or central cells and fibers. To state the 
case intelligibly, it is necessary to give something of the general 
physiological basis of normal responses. 
I have stated elsewhere my belief that the reactions of an 
animal generally occur in response to gvoups of afferent impulses 
of different kinds rather than to one single kind of afferent im- 
pulse. Jn looking over the field generally. I am more and more 
impressed with the number of responses in which afferent im- 
pulses from more than one source can be shown to participate. 
I am doubtful whether any single reflex response, particularly a 
response of the skeletal muscles, can be shown to involve affer- 
ent impulses from one source only. 
In making these statements, I am fully aware that in the 
elicitation of certain reflexes under experimental conditions, one 
