hemselves in the muscles. Those filaments or
cords are the nerves, which you know are divided into two kinds,
sensor and motor, or, if you like the terms better, afferent and
efferent nerves. The former carry impressions from the external world
to the brain; the latter convey the behests of the brain to the
muscles. Here, as elsewhere, we find ourselves aided by the sagacity
of Mayer, who was the first clearly to formulate the part played by
the nerves in the organism. Mayer saw that neither nerves nor brain,
nor both together, possessed the energy necessary to animal motion;
but he also saw that the nerve could lift a latch and open a door, by
which floods of energy are let loose. 'As an engineer,' he says with
admirable lucidity, 'by the motion of his finger in opening a valve or
loosening a detent can liberate an amount of mechanical energy almost
infinite compared with its exciting cause; so the nerves, acting on
the muscles, can unlock an amount of power out of all proportion to
the work done by the nerves themselves.' The nerves, according to
Mayer, pull the trigger, but the gunpowder which they ignite is stored
in the muscles. This is the view now universally entertained.

The quickness of thought has passed into a proverb, and the notion
that any measurable time elapsed between the infliction of a wound and
the feeling of the injury would have been rejected as preposterous
thirty years ago. Nervous impressions, notwithstanding the results of
Haller, were thought to be transmitted, if not instantaneously, at all
events with the rapidity of electricity. Hence, when Helmholtz, in
1851, affirmed, as the result of experiment, nervous transmission to
be a comparatively sluggish process, very few believed him. His
experiments may now be made in the lecture-room.

Sound in air moves at the rate of 1,100 feet a second; sound in water
moves at the rate of 5,000 feet a second; light in aether moves at the
rate of 186,000 miles a second, and electricity in free wires moves
probably at the same rate. But the nerves transmit their messages at
the rate of only 70 feet a second, a progress which in these quick
times might well be regarded as inordinately slow.

Your townsman, Mr. Gore, has produced by electrolysis a kind of
antimony which exhibits an action strikingly analogous to that of
nervous propagation. A rod of this antimony is in such a molecular
condition that when you scratch or heat one end of the rod, t