ccompany our perception of
extension. The whole set of muscles, whether they are hollow ones, as the
heart, arteries, and intestines, or longitudinal ones attached to bones,
contract themselves, whenever they are stimulated by forcible elongation;
and it is observable, that the white muscles, which constitute the arterial
system, seem to be excited into contraction from no other kinds of
stimulus, according to the experiments of Haller. And hence the violent
pain in some inflammations, as in the paronychia, obtains immediate relief
by cutting the membrane, that was stretched by the tumour of the subjacent
parts.

Hence the whole muscular system may be considered as one organ of sense,
and the various attitudes of the body, as ideas belonging to this organ, of
many of which we are hourly conscious, while many others, like the
irritative ideas of the other senses, are performed without our attention.

When the muscles of the heart cease to act, the refluent blood again
distends or elongates them; and thus irritated they contract as before. The
same happens to the arterial system, and I suppose to the capillaries,
intestines, and various glands of the body.

When the quantity of urine, or of excrement, distends the bladder, or
rectum, those parts contract, and exclude their contents, and many other
muscles by association act along with them; but if these evacuations are
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,