rtions, from which he experiences a temporary
relief. The same occurs in labour-pains, the exertion of the parturient
woman relieves the violence of the pains for a time, which recur again soon
after she has ceased to use those exertions. The same is true in many other
painful diseases, as in the strangury, tenesmus, and the efforts of
vomiting; all these disagreeable sensations are diminished or removed for a
time by the various exertions they occasion, and recur alternately with
those exertions.

The restlessness in some fevers is an almost perpetual exertion of this
kind, excited to relieve some disagreeable sensations; the reciprocal
opposite exertions of a wounded worm, the alternate emprosthotonos and
opisthotonos of some spasmodic diseases, and the intervals of all
convulsions, from whatever cause, seem to be owing to this circumstance of
the laws of animation; that great or universal exertion cannot exist at the
same time with great or universal sensation, though they can exist
reciprocally; which is probably resolvable into the more general law, that
the whole sensorial power being expended in one mode of exertion, there is
none to spare for any other. Whence syncope, or temporary apoplexy,
succeeds to epileptic convulsions.

3. Hence when any violent pain afflicts us, of which we can neither avoid
nor remove the cause, we soon learn to endeavour to alleviate it, by
exerting some violent voluntary effort, as mentioned above; and are
naturally induced to use those muscles for this purpose, which have been in
the early periods of our lives most frequently or most powerfully exerted.

Now the first muscles, which infants use most frequently, are those of
respiration; and on this account we gain a habit of holding our breath, at
the same time that we use great efforts to exclude it, for this purpose of
alleviating unavoidable pain; or we press out our breath through a small
aperture of the larynx, and scream violently, when the pain is greater than
is relievable by the former mode of exertion. Thus children scream to
relieve any pain either of body or mind, as from anger, or fear of being
beaten.

Hence it is curious to observe, that those animals, who have more
frequently exerted their muscles of respiration violently, as in talking,
barking, or grunting, as children, dogs, hogs, scream much more, when they
are in pain, than those other animals, who use little or no language in
their common modes of life; as ho