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 



