EXCITATION AND CONDUCTION 75 
the solution, but that it does not progress equally from 
the two ends. A distinct gradient in this change can be 
seen extending peripherally for a few millimeters from the 
central end and a shorter distance centrally from the 
peripheral end. This first change remains limited to 
the terminal regions of the nerve and is undoubtedly, 
as he interprets it, a temporary metabolic gradient from 
the ends inward, due to stimulation and injury resulting 
from severing the nerve at these points. Later, however, 
the fundamental metabolic gradient in the nerve appears, 
in that the change begins to progress along the nerve from 
the central toward the peripheral end; but the change at 
the peripheral end progresses but slowly, or not at all, 
in the central direction. From this time on a distinct 
gradient in the change is visible until it has progressed 
along the whole length of the nerve. Except in the ter- 
minal region adjoining the peripheral cut end the death 
change always progresses in the peripheral direction. 
The peripheral third of the length may be entirely 
unchanged at a time when the central third or more has 
completely lost the fibrillar appearance. Thus the fun- 
damental difference of the two ends is made apparent. 
Child has further shown that if the nerve is crushed 
or injured at any point similar gradients appear on both 
sides of the injury, but do not extend to a great distance 
before the general change reaches this region in its 
progress peripherally. 
Since it has been demonstrated repeatedly that 
susceptibility of other tissues and organisms to reagents 
like ether and cyanide is an expression of the rate of 
metabolism in the tissue, these results of Child not 
only confirm our demonstration that there is a clear 
