178 
On the Active Part of the Nerve Fibre, 
transmission of different kinds of nerve force. One would have 
thought that it would be more in accordance with the doctrines of 
physical science to endeavour to explain the phenomena by the 
action of forces we know something about, than to attribute them 
to the influence of other forms or modes of force which are purely 
fanciful and fictitious. At any rate it will be time to call in the 
aid of such airy nothings when all attempts to explain the facts by 
known forces shall have failed. 
But it is interesting to notice how often minds of the most 
rigidly physical tendencies seize upon purely conjectural hypotheses, 
and use them as if they were established truths. It has been 
surmised that nerve action depends upon a chemical change which 
is supposed to take place in every part of the nerve fibre. 
Mr. Herbert Spencer settles the question in the most summary way 
by boldly asserting that the axis cylinder of a nerve consists of 
some colloid “ matter isomerically transformed with ease.” He 
accounts for nerve action by suggesting that the protein substance 
of the axis cylinder “ is habitually changed from one of its isomeric 
states to another,” while he says that the matter of the nerve cell 
is the seat “of destructive molecular changes and disengagement 
of motion.” 
Chemical Theory of the Nerve Current. 
A chemical theory was long held concerning the nature of 
muscular action, hut it was at last admitted, as was, indeed, apparent 
from the very first, that muscles would have to be destroyed and 
reformed at a far more rapid rate than it was on other grounds 
reasonable to suppose possible, if the great amount of energy mani- 
fested during their action was really due to chemical decomposition 
of the tissue of the muscle itself. There was, in fact, no evidence 
whatever, except that which was distilled from the imagination of 
the chemist, for the conclusion that muscular tissue did undergo 
rapid disintegration and reconstruction. From my own investiga- 
tions of muscular fibres in various animals, I felt quite sure at the 
very time when these chemical doctrines were in high favour, that 
the conclusions were thoroughly erroneous. From the study of 
muscular tissue at different periods of development, and the con- 
sideration of various circumstances connected with the growth of 
muscle and its relation to other textures in a variety of animals, 
particularly in the class of insects, I was convinced that muscle 
was a sloidy growing tissue, and that the work it performed was 
certainly not due to the chemical decomposition of its material 
particles. Nevertheless the fact of the change in the reaction of 
muscle from alkaline to acid is still urged in favour of the doctrine, 
and some have affirmed that a similar change occurs in nerve. In 
