p a part or the
whole of these fluids, and carry them forwards by their living power to
their respective glands, which are called conglobate glands. There these
fluids undergo some change, before they pass on into the circulation; but
if they are very acrid, the conglobate gland swells, and sometimes
suppurates, as in inoculation of the small-pox, in the plague, and in
venereal absorptions; at other times the fluid may perhaps continue there,
till it undergoes some chemical change, that renders it less noxious; or,
what is more likely, till it is regurgitated by the retrograde motion of
the gland in spontaneous sweats or diarrhoeas, as disagreeing food is
vomited from the stomach.

IV. As all the fluids, that pass through these glands, and capillary
vessels, undergo a chemical change, acquiring new combinations, the matter
of heat is at the same time given out; this is apparent, since whatever
increases insensible perspiration, increases the heat of the skin; and when
the action of these vessels is much increased but for a moment, as in
blushing, a vivid heat on the skin is the immediate consequence. So when
great bilious secretions, or those of any other gland, are produced, heat
is generated in the part in proportion to the quantity of the secretion.

The heat produced on the skin by blushing may be thought by some too sudden
to be pronounced a chemical effect, as the fermentations or new
combinations taking place in a fluid is in general a slower process. Yet
are there many chemical mixtures in which heat is given out as
instantaneously; as in solutions of metals in acids, or in mixtures of
essential oils and acids, as of oil of cloves and acid of nitre. So the
bruised parts of an unripe apple become almost instantaneously sweet; and
if the chemico-animal process of digestion be stopped for but a moment, as
by fear, or even by voluntary eructation, a great quantity of air is
generated, by the fermentation, which instantly succeeds the stop of
digestion. By the experiments of Dr. Hales it appears, that an apple during
fermentation gave up above six hundred times its bulk of air; and the
materials in the stomach are such, and in such a situation, as immediately
to run into fermentation, when digestion is impeded.

As the blood passes through the small vessels of the lungs, which connect
the pulmonary artery and vein, it undergoes a change of colour from a dark
to a light red; which may be termed a chemical change, as