sack, than the puncta lacrymalia can imbibe. Of the
gout in the liver and stomach._

I. The salival glands drink up a certain fluid from the circumfluent blood,
and pour it into the mouth. They are sometimes stimulated into action by
the blood, that surrounds their origin, or by some part of that
heterogeneous fluid: for when mercurial salts, or oxydes, are mixed with
the blood, they stimulate these glands into unnatural exertions; and then
an unusual quantity of saliva is separated.

1. As the saliva secreted by these glands is most wanted during the
mastication of our food, it happens, when the terminations of their ducts
in the mouth are stimulated into action, the salival glands themselves are
brought into increased action at the same time by association, and separate
a greater quantity of their juices from the blood; in the same manner as
tears are produced in greater abundance during the stimulus of the vapour
of onions, or of any other acrid material in the eye.

The saliva is thus naturally poured into the mouth only during the stimulus
of our food in mastication; for when there is too great an exhalation of
the mucilaginous secretion from the membranes, which line the mouth, or too
great an absorption of it, the mouth becomes dry, though there is no
deficiency in the quantity of saliva; as in those who sleep with their
mouths open, and in some fevers.

2. Though during the mastication of our natural food the salival glands are
excited into action by the stimulus on their excretory ducts, and a due
quantity of saliva is separated from the blood, and poured into the mouth;
yet as this mastication of our food is always attended with a degree of
pleasure; and that pleasurable sensation is also connected with our ideas
of certain kinds of aliment; it follows, that when these ideas are
reproduced, the pleasurable sensation arises along with them, and the
salival glands are excited into action, and fill the mouth with saliva from
this sensitive association, as is frequently seen in dogs, who slaver at
the sight of food.

3. We have also a voluntary power over the action of these salival glands,
for we can at any time produce a flow of saliva into our mouth, and spit
out, or swallow it at will.

4. If any very acrid material be held in the mouth, as the root of
pyrethrum, or the leaves of tobacco, the salival glands are stimulated into
stronger action than is natural, and thence secrete a much larger quantity