completely under our command.
When we are conscious of the presence of an irritating particle in our
nostrils or windpipe that is, when the same sensory nerve-cells are
excited, as in the case of sneezing and coughing we can voluntarily
expel the particle by forcibly driving air through these passages; but
we cannot do this with nearly the same force, rapidity, and precision,
as by a reflex action. In this latter case the sensory nerve-cells
apparently excite the motor nerve-cells without any waste of power by
first communicating with the cerebral hemispheres the seat of our
consciousness and volition. In all cases there seems to exist a
profound antagonism between the same movements, as directed by the will
and by a reflex stimulant, in the force with which they are performed
and in the facility with which they are excited. As Claude Bernard
asserts, L influence du cerveau tend donc a entraver les mouvements
reflexes, a limiter leur force et leur etendue. [111]
The conscious wish to perform a reflex action sometimes stops or
interrupts its performance, though the proper sensory nerves may be
stimulated. For instance, many years ago I laid a small wager with a
dozen young men that they would not sneeze if they took snuff, although
they all declared that they invariably did so; accordingly they all
took a pinch, but from wishing much to succeed, not one sneezed, though
their eyes watered, and all, without exception, had to pay me the
wager. Sir H. Holland remarks[112] that attention paid to the act of
swallowing interferes with the proper movements; from which it probably
follows, at least in part, that some persons find it so difficult to
swallow a pill.
Another familiar instance of a reflex action is the involuntary closing
of the eyelids when the surface of the eye is touched. A similar
winking movement is caused when a blow is directed towards the face;
but this is an habitual and not a strictly reflex action, as the
stimulus is conveyed through the mind and not by the excitement of a
peripheral nerve. The whole body and head are generally at the same
time drawn suddenly backwards. These latter movements, however, can be
prevented, if the danger does not appear to the imagination imminent;
but our reason telling us that there is no danger does not suffice. I
may mention a trifling fact, illustrating this point, and which at the
time amused me. I put my face close to the thick glass-plate in front
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