504 F. H. PIKE 
remember, either, that he used the term vicarious assumption of 
function. It is true that Jackson was not an experimentalist, 
but his powers of observation and of deducing from his facts a 
generalization which would hold them all together were extra- 
ordinary. In the matter of cerebral localization, he anticipated 
by several years the experimental work of Fritsch and Hitzig. 
The idea of a change of energy in the remaining levels of the 
central nervous system should, from its authorship, command at 
least a careful scrutiny. But aside from some of the fruitful 
suggestions of Luciani, I have seen little or no use made of the 
hypothesis by experimentalists, despite the fact that such a 
hypothesis might be given the rank of a fundamental assumption. 
I am strongly of the opinion at present that we have experi- 
mental proof that a given conduction pathway may carry a 
greater quantity of nervous energy after injury to another path 
way associated with it in the control of a given response than it 
carries under the usual conditions.* 
3 Prof. W. M. Bayliss, who has read the manuscript, has asked me just what 
the earlier statement of Jackson about the change in the quantity of nerve energy 
passing over a given pathway might mean in terms of the recent work of Lucas 
and Adrian on the nerve impulse. One may take as an example of such a change 
the crossing over of efferent impulses from the respiratory center at the phrenic 
nuclei. (Porter, Journal of Physiology, 1894-5, 17, p. 455). The reader must 
consult the original paper for the full description of the phenomena, as it is too 
long to give here in detail. When the spinal cord is hemisected above the level 
of origin of the phrenic nerve, we will say on the right side, the movements of 
the half of the diaphragm on that side cease. If the phrenic nerve of the oppo- 
site (uninjured or left) side is divided, the movements of the right half of the 
diaphragm begin again. The impulses which were passing down the left side of 
the cord now cross to the right side. As I see it, there is a change in the quan- 
tity of nervous energy passing over the commissural fibers and synapses from the 
left phrenic nucleus to the right. It is possible, even probable, that the increas- 
ing asphyxial condition which comes on after section of the left phrenic nerve 
leads to the excitation of more cells in the bulbar respiratory center and to the 
sending out of impulses over more efferent fibers than before. It is not necessary 
to postulate any increase in the intensity of the impulses coming over any 
one fiber. In view of Stirling’s demonstration that the synapses have the power 
of summation of impulses, and Sherrington’s experiments, as well as observations 
by G. N. Stewart and myself, pointing to the same conclusion, I think it probable 
that the principal change occurs in the passability of the synapses. In the com- 
pensations occurring after loss of the otic labyrinth, it does not seem possible 
that either more fibers are excited in any of the afferent systems entering 
