dissevered by irritations, by volition, production of surprise._

I. 1. To investigate with precision the catenations of animal motions, it
would be well to attend to the manner of their production; but we cannot
begin this disquisition early enough for this purpose, as the catenations
of motion seem to begin with life, and are only extinguishable with it; We
have spoken of the power of irritation, of sensation, of volition, and of
association, as preceding the fibrous motions; we now step forwards, and
consider, that conversely they are in their turn preceded by those motions;
and that all the successive trains or circles of our actions are composed
of this twofold concatenation. Those we shall call trains of action, which
continue to proceed without any stated repetitions; and those circles of
action, when the parts of them return at certain periods, though the
trains, of which they consist, are not exactly similar. The reading an epic
poem is a train of actions; the reading a song with a chorus at equal
distances in the measure constitutes so many circles of action.

2. Some catenations of animal motion are produced by reiterated successive
irritations, as when we learn to repeat the alphabet in its order by
frequently reading the letters of it. Thus the vermicular motions of the
bowels were originally produced by the successive irritations of the
passing aliment; and the succession of actions of the auricles and
ventricles of the heart was originally formed by successive stimulus of the
blood, these afterwards become part of the diurnal circles of animal
actions, as appears by the periodical returns of hunger, and the quickened
pulse of weak people in the evening.

Other catenations of animal motion are gradually acquired by successive
agreeable sensations, as in learning a favourite song or dance; others by
disagreeable sensations, as in coughing or nictitation; these become