their animal action, draw the limb into a contrary
direction: in the solid muscles, as those of locomotion, their actions are
associated in tribes, which have been accustomed to synchronous action
only; hence when they are fatigued, only a single contrary effort takes
place; which is either tremulous, when the fatigued muscles are again
immediately brought into action; or it is a pandiculation, or stretching,
where they are not immediately again brought into action.

Now the motions of the hollow muscles, as they in general propel a fluid
along their cavities, are associated in trains, which have been accustomed
to successive actions: hence when one ring of such a muscle is fatigued
from its too great debility, and is brought into retrograde action, the
next ring from its association falls successively into retrograde action;
and so on throughout the whole canal. See Sect. XXV. 6.

6. But as the retrograde motions of the stomach, oesophagus, and fauces in
vomiting are, as it were, apparent to the eye; we shall consider this
operation more minutely, that the similar operations in the more recondite
parts of our system may be easier understood.

From certain nauseous ideas of the mind, from an ungrateful taste in the
mouth, or from foetid smells, vomiting is sometimes instantly excited; or
even from a stroke on the head, or from the vibratory motions of a ship;
all which originate from association, or sympathy. See Sect. XX. on
Vertigo.

But when the stomach is subjected to a less stimulus than is natural,
according to the first law of irritation mentioned above, its motions
become disturbed, as in hunger; first pain is produced, then sickness, and
at length vain efforts to vomit, as many authors inform us.

But when a great quantity of wine, or of opium, is swallowed, the
retrograde motions of the stomach do not occur till after several minutes,
or even hours; for when the power of so strong a stimulus ceases, according
to the second law of irritation, mentioned above, the peristaltic motions
become tremulous, and at length retrograde; as is well known to the
drunkard, who on the next morning has sickness and vomitings.

When a still greater quantity of wine, or of opium, or when nauseous
vegetables, or strong bitters, or metallic salts, are taken into the
stomach, they quickly induce vomiting; though all these in less doses
excite the stomach into more energetic action, and strengthen the
digestion; as the flowers