hardness with inequality.

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.