a more perfect sanguification in the
lungs, and, in short, gives strength and vigour to every function of
the body. Hence it is, that the Author of nature has made exercise
absolutely necessary to the greater part of mankind for obtaining
means of existence. Had not exercise been absolutely necessary for
our well being, says the elegant Addison, nature would not have made
the body so proper for it, by giving such an activity to the limbs,
and such a pliancy to every part, as necessarily produce those
compressions, extensions, contortions, dilatations, and all other
kinds of motion, as are necessary for the preservation of such a
system of tubes and glands.

We may, indeed, observe, that nature has never given limbs to any
animal, without intending that they should be used. To fish she has
given fins, and to the fowls of the air wings, which are incessantly
used in swimming and flying; and if she had destined mankind to be
eternally dragged about by horses, her provident economy would surely
have denied them legs.

The appetite becomes deficient on the commencement of many diseases,
but this is to be looked upon here rather as a salutary than as a
morbid symptom, and as a proof that nature refuses the load, which
she can neither digest nor bear with impunity.

In healthy people the appetite is various, some requiring more food
than others; but it sometimes becomes praeternaturally great, and
then may be regarded as a morbid symptom. The appetite may be
praeternaturally increased, either by an unusual secretion of the
gastric juice, which acts upon the coats of the stomach, or by any
acrimony, either generated in, or received into the stomach, or,
lastly, by habit, for people undoubtedly may gradually accustom
themselves to take more food than is necessary.

The appetite sometimes becomes depraved, and a person thus affected,
feels a desire to eat substances that are by no means nutritious, or
even esculent: this often depends on a debilitated state of the whole
system. There are some instances, however, in which this depravity of
the appetite is salutary; for example, the great desire which some
persons, whose stomachs abound with acid, have for eating chalk, and
other absorbent earths: likewise, the desire which scorbutic patients
have for grass, and other fresh vegetables. Appetites of this kind,
if moderately indulged in, are salutary, rather than hurtful.

The appetite for liquids as well as solids is sometime