not soon complied with, pain is produced by a little further extension of
the muscular fibres: a similar pain is caused in the muscles, when a limb
is much extended for the reduction of dislocated bones; and in the
punishment of the rack: and in the painful cramps of the calf of the leg,
or of other muscles, for a greater degree of contraction of a muscle, than
the movement of the two bones, to which its ends are affixed, will admit
of, must give similar pain to that, which is produced by extending it
beyond its due length. And the pain from punctures or incisions arises from
the distention of the fibres, as the knife passes through them; for it
nearly ceases as soon as the division is completed.

All these motions of the muscles, that are thus naturally excited by the
stimulus of distending bodies, are also liable to be called into strong
action by their catenation, with the irritations or sensations produced by
the momentum of the progressive particles of blood in the arteries, as in
inflammatory fevers, or by acrid substances on other sensible organs, as in
the strangury, or tenesmus, or cholera.

We shall conclude this account of the sense of extension by observing, that
the want of its object is attended with a disagreeable sensation, as well
as the excess of it. In those hollow muscles, which have been accustomed to
it, this disagreeable sensation is called faintness, emptiness, and
sinking; and, when it arises to a certain degree, is attended with syncope,
or a total quiescence of all motions, but the internal irritative ones, as
happens from sudden loss of blood, or in the operation of tapping in the
dropsy.

VIII. _Of the Appetites of Hunger, Thirst, Heat, Extension, the want of
fresh Air, animal Love, and the Suckling of Children._