10. If a train of actions is dissevered, much effort of volition or
sensation will prevent its being restored. Thus in the common impediment of
speech, when the association of the motions of the muscles of enunciation
with the idea of the word to be spoken is disordered, the great voluntary
efforts, which distort the countenance, prevent the rejoining of the broken
associations. See No. II. 10. of this Section. It is thus likewise
observable in some inflammations of the bowels, the too strong efforts made
by the muscles to carry forwards the offending material fixes it more
firmly in its place, and prevents the cure. So in endeavouring to recal to
our memory some particular word of a sentence, if we exert ourselves too
strongly about it, we are less likely to regain it.

11. Catenated trains or tribes of action are easier dissevered than
catenated circles of action. Hence in epileptic fits the synchronous
connected tribes of action, which keep the body erect, are dissevered, but
the circle of vital motions continues undisturbed.

12. Sleep destroys the power of volition, and precludes the stimuli of
external objects, and thence dissevers the trains, of which these are a
part; which confirms the other catenations, as those of the vital motions,
secretions, and absorptions; and produces the new trains of ideas, which
constitute our dreams.

II. 1. All the preceding circumstances of the catenations of animal motions
will be more clearly understood by the following example of a person
learning music; and when we recollect the variety of mechanic arts, which
are performed by associated trains of muscular actions catenated with the
effects they produce, as in knitting, netting, weaving; and the greater
variety of associated trains of ideas caused or catenated by volitions or
sensations, as in our hourly modes of reasoning, or imagining, or