A start from a sudden noise, when the stimulus is conveyed through the
auditory nerves, is always accompanied in grown-up persons by the winking
of the eyelids.[13] I observed, however, that though my infants started
at sudden sounds, when under a fortnight old, they certainly did not always
wink their eyes, and I believe never did so. The start of an older infant
apparently represents a vague catching hold of something to prevent falling.
I shook a pasteboard box close before the eyes of one of my infants, when 114
days old, and it did not in the least wink; but when I put a few comfits
into the box, holding it in the same position as before, and rattled them,
the child blinked its eyes violently every time, and started a little.
It was obviously impossible that a carefully-guarded infant could have learnt
by experience that a rattling sound near its eyes indicated danger to them.
But such experience will have been slowly gained at a later age during
a long series of generations; and from what we know of inheritance,
there is nothing improbable in the transmission of a habit to the offspring
at an earlier age than that at which it was first acquired by the parents.

From the foregoing remarks it seems probable that some actions,
which were at first performed consciously, have become
through habit and association converted into reflex actions,
and are now so firmly fixed and inherited, that they
are performed, even when not of the least use,[14] as often
as the same causes arise, which originally excited them in us
through the volition. In such cases the sensory nerve-cells
excite the motor cells, without first communicating with
those cells on which our consciousness and volition depend.
It is probable that sneezing and coughing were originally
acquired by the habit of expelling, as violently as possible,
any irritating particle from the sensitive air-passages. As far
as time is concerned, there has been more than enough for these