have once occurred in succession, or in combination, should afterwards have
a tendency to succeed or accompany each other. It is a property of
animation, and distinguishes this order of being from the other productions
of nature.

When a child first wrote the word man, it was distinguished in his mind
into three letters, and those letters into many parts of letters; but by
repeated use the word man becomes to his hand in writing it, as to his
organs of speech in pronouncing it, but one movement without any
deliberation, or sensation, or irritation, interposed between the parts of
it. And as many separate motions of our muscles thus become united, and
form, as it were, one motion; so each separate motion before such union may
be conceived to consist of many parts or spaces moved through; and perhaps
even the individual fibres of our muscles have thus gradually been brought
to act in concert, which habits began to be acquired as early as the very
formation of the moving organs, long before the nativity of the animal; as
explained in the Section XVI. 2. on instinct.

2. There are many motions of the body, belonging to the irritative class,
which might by a hasty observer be mistaken for associated ones; as the
peristaltic motion of the stomach and intestines, and the contractions of
the heart and arteries, might be supposed to be associated with the
irritative motions of their nerves of sense, rather than to be excited by
the irritation of their muscular fibres by the distention, acrimony, or
momentum of the blood. So the distention or elongation of muscles by
objects external to them irritates them into contraction, though the
cuticle or other parts may intervene between the stimulating body and the
contracting muscle. Thus a horse voids his excrement when its weight or
bulk irritates the rectum or sphincter ani. These muscles act from the
irritation of distention, when he excludes his excrement, but the muscles