and on the 'probable Nature of the Nerve Current. 179 
spite of the statements of Liebreich, ITeidenhain, and other observers 
to the direct contrary, the view that nerve energy is stored up in 
chemical compounds which undergo chemical change during nerve 
action is still taught. That such an idea should be stated at all 
betrays ignorance of the character of the axis cylinder of the nerve 
itself. If we examine the axis cylinder, say, of the sciatic nerve of 
a frog, what do we find? — a firm, tough, fibrous-like, flattened 
band, not easily torn, and evidently consisting of a tissue of slow 
growth ; in fact, the very last characters we should expect to find 
in a tissue prone to rapid chemical change. Neither is a structure 
surrounded by ten times its thickness of oily matter (myelin) 
favourably situated for taking up new materials and quickly getting 
rid of products of decay. One of the least permeable substances in 
the body is the myelin of the nerve fibre, and yet through this must 
pass all the materials from the blood to renovate the disintegrated 
axis cylinder, if nerve action is due to chemical change in the nerve 
fibre itself. 
The Vibratory Theory of Nerve Action. 
Some think that nerve action depends upon the molecules of 
nerve fibres being thrown into vibration, and the axis cylinder of a 
nerve has been spoken of as if it had been proved to consist of 
a chain or chains of very minute spherical particles. But the axis 
cylinder is not composed of matter which would more readily 
propagate motor impulses than the matter of ordinary fibrous 
tissue. Moreover, it varies much in character and in thickness in 
different parts of its course. The impulses supposed would be much 
modified during their transmission. This theory leaves one of the 
most important facts connected with nerve fibres unexplained ; for 
upon such a supposition what purpose could be served by the very 
thick layer of the white substance of Schwann, and in that part of 
the nerve only which lies between its central and peripheral distri- 
bution ? Why do we find, moreover, that this investment is invari- 
ably so much thicker where a number of nerves run for a long 
distance parallel to one another than where they cross one another 
at considerable angles ? 
Experimental Investigation Inconclusive. 
Most of those who have taken up the subject of nerve action 
from the experimental side, appear to have had a very imperfect 
acquaintance with the structure of the tissue upon which they were 
experimenting. The transmission of electric currents through the 
nerves of a recently-killed animal, is a very rough operation, and 
indeed very different in many particulars from the transmission of 
the natural currents, whatever may be their nature, along the axis 
