this semi-automatic way unhesitatingly and efficiently, the very
outermost margin of consciousness seeming to be concerned in them,
while the focus may be occupied with widely different things.

But now turn to a more complicated case. Suppose two thoughts to be in
the mind together, of which one, A, taken alone, would discharge itself
in a certain action, but of which the other, B, suggests an action of a
different sort, or a consequence of the first action calculated to make
us shrink. The psychologists now say that the second idea, B, will
probably arrest or _inhibit_ the motor effects of the first idea, A. One
word, then, about 'inhibition' in general, to make this particular case
more clear.

One of the most interesting discoveries of physiology was the discovery,
made simultaneously in France and Germany fifty years ago, that nerve
currents do not only start muscles into action, but may check action
already going on or keep it from occurring as it otherwise might.
_Nerves of arrest_ were thus distinguished alongside of motor nerves.
The pneumogastric nerve, for example, if stimulated, arrests the
movements of the heart: the splanchnic nerve arrests those of the
intestines, if already begun. But it soon appeared that this was too
narrow a way of looking at the matter, and that arrest is not so much
the specific function of certain nerves as a general function which any
part of the nervous system may exert upon other parts under the
appropriate conditions. The higher centres, for example, seem to exert a
constant inhibitive influence on the excitability of those below. The
reflexes of an animal with its hemispheres wholly or in part removed
become exaggerated. You all know that common reflex in dogs, whereby, if
you scratch the animal's side, the corresponding hind leg will begin to
make scratching movements, usually in the air. Now in dogs with
mutilated hemispheres this scratching reflex is so incessant that, as
Goltz first described them, the hair gets all worn off their sides. In
idiots, the functions of the hemispheres being largely in abeyance, the
lower impulses, not inhibited, as they would be in normal human beings,
often express themselves in most odious ways. You know also how any
higher emotional tendency will quench a lower one. Fear arrests
appetite, maternal love annuls fear, respect checks sensuality, and the
like; and in the more subtile manifestations of the moral life, whenever
an ideal stirring