produced. Here the desire of moving the body is painfully exerted, by the
power of moving it, or volition, is incapable of action, till we awake.
Many less disagreeable struggles in our dreams, as when we wish in vain to
fly from terrifying objects, constitute a slighter degree of this disease.
In awaking from the nightmare I have more than once observed, that there
was no disorder in my pulse; nor do I believe the respiration is laborious,
as some have affirmed. It occurs to people whose sleep is too profound, and
some disagreeable sensation exists, which at other times would have
awakened them, and have thence prevented the disease of nightmare; as after
great fatigue or hunger with too large a supper and wine, which occasion
our sleep to be uncommonly profound. See No. 14, of this Section.

4. As the larger muscles of the body are much more frequently excited by
volition than by sensation, they are but seldom brought into action in our
sleep: but the ideas of the mind are by habit much more frequently
connected with sensation than with volition; and hence the ceaseless flow
of our ideas in dreams. Every one's experience will teach him this truth,
for we all daily exert much voluntary muscular motion: but few of mankind
can bear the fatigue of much voluntary thinking.

5. A very curious circumstance attending these our sleeping imaginations
is, that we seem to receive them by the senses. The muscles, which are
subservient to the external organs of sense, are connected with volition,
and cease to act in sleep; hence the eyelids are closed, and the tympanum
of the ear relaxed; and it is probable a similarity of voluntary exertion
may be necessary for the perceptions of the other nerves of sense; for it
is observed that the papillæ of the tongue can be seen to become erected,
when we attempt to taste any thing extremely grateful. Hewson Exper.
Enquir. V. 2. 186. Albini Annot. Acad. L. i. c. 15. Add to this, that the
immediate organs of sense have no objects to excite them in the darkness