t. When gratified, it ceases for a time, and is
renewed for the same person nearly at the same intervals, and under
similar circumstances. It is, while it lasts, an uneasy, even a painful
sensation, and therefore demands prompt relief, and leads to action with a
view to such relief. It is also a characteristic of appetite that its
indulgence is attended, not merely by relief, but by positive pleasure.

The appetites are essential to the well-being of men, individually and
collectively. Were it not for the pain of hunger and thirst, and the
pleasure of gratifying them, both indolence and engrossing industry would
draw off the attention of men from their bodily needs; nourishment would
be taken irregularly, and with little reference to quality; and one would
often become aware of his neglect only too late to arrest its
consequences. A similar remark applies to the appetite designed to secure
the preservation of the species. But for this, it may be doubted whether
men would willingly take upon themselves the cares, labors,
responsibilities, and contingent disappointments and sorrows involved in
the rearing of children.

In a life conformed to nature, hunger and thirst recur only when the body
actually needs the supply which they crave. But stimulating food, by the
reaction that follows strong excitement of any portion of the nervous
system, may create hunger when there is no need of food, and in like
manner not only intoxicating, but highly stimulating liquids, may occasion
an excessive, morbid, and injurious thirst.

Appetite is modified by habit. There is hardly any substance so offensive
that it may not by use become agreeable, then an object of desire, and, at
length, of intense craving.

The craving for repose and that for muscular action, though not classed
among the appetites, have all their characteristics, and serve similar
ends in the economy of human life. After a certain period of activity,
rest is felt as a bodily necessity, as food is, after long fasting; and in
like manner, when the wearied muscles have had their due repose, there is
an irresistible tendency to their exercise, without reference to any
special employment or recreation. It is by the alternation of these
tendencies that the active and industrious are saved from the ruinous
consequences of overtasked limbs or brain, and that the indolent are urged
to the reluctant activity without which health and life itself would be
sacrificed.

The appet