Pleasure and pain are the most important of the affections common
to the whole body. According to our general doctrine of
sensation, parts of the body which are easily moved readily
transmit the motion to the mind; but parts which are not easily
moved have no effect upon the patient. The bones and hair are of
the latter kind, sight and hearing of the former. Ordinary
affections are neither pleasant nor painful. The impressions of
sight afford an example of these, and are neither violent nor
sudden. But sudden replenishments of the body cause pleasure, and
sudden disturbances, as for example cuttings and burnings, have
the opposite effect.
>From sensations common to the whole body, we proceed to those of
particular parts. The affections of the tongue appear to be
caused by contraction and dilation, but they have more of
roughness or smoothness than is found in other affections. Earthy
particles, entering into the small veins of the tongue which
reach to the heart, when they melt into and dry up the little
veins are astringent if they are rough; or if not so rough, they
are only harsh, and if excessively abstergent, like potash and
soda, bitter. Purgatives of a weaker sort are called salt and,
having no bitterness, are rather agreeable. Inflammatory bodies,
which by their lightness are carried up into the head, cutting
all that comes in their way, are termed pungent. But when these
are refined by putrefaction, and enter the narrow veins of the
tongue, and meet there particles of earth and air, two kinds of
globules are formed—one of earthy and impure liquid, which boils
and ferments, the other of pure and transparent water, which are
called bubbles; of all these affections the cause is termed acid.
When, on the other hand, the composition of the deliquescent
particles is congenial to the tongue, and disposes the parts
according to their nature, this remedial power in them is called
sweet.
Smells are not divided into kinds; all of them are transitional,
and arise out of the decomposition of one element into another,
for the simple air or water is without smell. They are vapours or
mists, thinner than water and thicker than air: and hence in
drawing in the breath, when there is an obstruction, the air
passes, but there is no smell. They have no names, but are
distinguished as pleasant and unpleasant, and their influence
extends over the whole region from the head to the navel.