this the unceasing injury which accrues to the public by the perpetual
advertisements of pretended nostrums; the minds of the indolent become
superstitiously fearful of diseases, which they do not labour under; and
thus become the daily prey of some crafty empyric.

A theory founded upon nature, that should bind together the scattered facts
of medical knowledge, and converge into one point of view the laws of
organic life, would thus on many accounts contribute to the interest of
society. It would capacitate men of moderate abilities to practise the art
of healing with real advantage to the public; it would enable every one of
literary acquirements to distinguish the genuine disciples of medicine from
those of boastful effrontery, or of wily address; and would teach mankind
in some important situations the _knowledge of themselves_.

There are some modern practitioners, who declaim against medical theory in
general, not considering that to think is to theorize; and that no one can
direct a method of cure to a person labouring under disease without
thinking, that is, without theorizing; and happy therefore is the patient,
whose physician possesses the best theory.

The words idea, perception, sensation, recollection, suggestion, and
association, are each of them used in this treatise in a more limited sense
than in the writers of metaphysic. The author was in doubt, whether he
should rather have substituted new words instead of them; but was at length
of opinion, that new definitions of words already in use would be less
burthensome to the memory of the reader.

A great part of this work has lain by the writer above twenty years, as
some of his friends can testify: he had hoped by frequent revision to have
made it more worthy the acceptance of the public; this however his other