Before proceeding further it will be necessary first to obtain a clear
idea of the function of a nervous tissue and its characteristics;
secondly the manner, in which the nervous impulse is propagated; and
lastly, we have to discover some compulsive force by which the impulse
may be intensified or inhibited during transit. The nerve circuit may be
liked to an electric circuit, and invisible impulse bringing about
response in the indicator, be it the brain or the galvanometer. In the
electric circuit the conducting power of the metallic wire is constant,
and the intensity of the electric impulse depends on the intensity of
the electric force applied. If the conducting power of the nerve were
constant then the intensity of the nervous impulse and its resulting
sensation would depend inevitably on the intensity of the shock from
outside which starts the impulse. In that case the possibility of the
modification of our sensation would be an impossibility. But there may
be a likelihood that the power of conduction possessed by a nerve is
not constant but capable of change. Should this surmise prove to be
correct then we arrive at the momentous conclusion that sensation itself
is modifiable, whatever the external stimulus. For the modification of
nervous impulse there remains only one alternative; namely, some power
to render the vehicle a very much better conductor or a non-conductor
according to particular requirements. We require the nervous path to the
supra-conducting to have the impulse due to feeble stimulus brought to
sensory prominence. When the external blow is too violent we would block
the painful impulse by rendering the nerve a non-conductor.
Under narcotic the nerve becomes paralysed and we can by its use save
ourselves from pain. But such heroic measures are to be resorted to in
extreme cases, as when we are under the surgeon's knife. In actual life
we are confronted with unpleasantness without notice. A telephone
subscriber has an evident advantage, for he can switch off the
connection when the message begins to be unpleasant. Statesmen or
politicians have been known to cultivate convenient deafness; but that
is a mere pretence. The unpleasant things heard, would still continue to
rankle. It is not every one that has the courage of Mr. Herbert Spencer
who openly resorted to his ear plugs whenever his visitor became
tedious.
The lecturer then explained that the propagation of nervous impulse is a
phenomenon of transmission of molecular disturbance. It occurred to him
that the transmission could be controlled if he succeeded in discovering
a compulsive force which would confer on the conducting particles two
opposite molecular dispositions, one of which would exalt and the other
resist the impulse. His experiments were first conducted with the
primitive type of nerve which he had previously discovered in plants. In
full confirmation of his theory, he succeeded in conferring on the
nervous tissue two opposite dispositions. Under favourable disposition
the nerve is rendered supra-conducting; subliminal stimulus now becomes
fully perceived. Under the opposite molecular disposition the violent
impulse due to excessive stimulus becomes weakened or arrested during
transit, and the plant remains quite unaffected by the external shock.
The lecturer has in his previous works demonstrated the unity of
life-reactions in the plant and animal. A climax is now reached when by
the application of identical treatment he is able to confer alternately
on the same animal nerve, supra-conducting or non-conducting property at
will. Under a particular molecular disposition the experimental frog
perceived and responded to stimulus which had hitherto been below its
threshold of perception. Under the opposite disposition violent tetanic
spasm caused by the irritant salt applied to the nerve became at once
quelled. The normal property of the nerve was at once restored on the
withdrawal of the predisposing force.