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PREFACE.

All diseases originate in the exuberance, deficiency, or retrograde action,
of the faculties of the sensorium, as their proximate cause; and consist in
the disordered motions of the fibres of the body, as the proximate effect
of the exertions of those disordered faculties.

The sensorium possesses four distinct powers, or faculties, which are
occasionally exerted, and produce all the motions of the fibrous parts of
the body; these are the faculties of producing fibrous motions in
consequence of irritation which is excited by external bodies; in
consequence of sensation which is excited by pleasure or pain; in
consequence of volition which is excited by desire or aversion; and in
consequence of association which is excited by other fibrous motions. We
are hence supplied with four natural classes of diseases derived from their
proximate causes; which we shall term those of irritation, those of
sensation, those of volition, and those of association.

In the subsequent classification of diseases I have not adhered to the
methods of any of those, who have preceded me; the principal of whom are
the great names of Sauvages and Cullen; but have nevertheless availed
myself, as much as I could, of their definitions and distinctions.

The essential characteristic of a disease consists in its proximate cause,
as is well observed by Doctor Cullen, in his Nosologia Methodica, T. ii.
Prolegom. p. xxix. Similitudo quidem morborum in similitudine causae eorum
proximae, qualiscunque sit, revera consistit. I have taken the proximate
cause for the classic character. The characters of the orders are taken
from the excess, or deficiency, or retrograde action, or other properties
of the proximate cause. The genus is generally derived from the proximate
effect. And the species generally from the locality of the disease in the
system.

Many species in this system are termed genera in the systems of other
writers; and the species of those writers are in consequence here termed
varieties. Thus in Dr. Cullen's Nosologia the variola or small-pox is
termed a genus, and the distinct and confluent kinds are termed species.
But as the infection from the distinct kind frequently produces the
confluent kind, and that of the confluent kind frequently produces the
distinct; it would seem more analogous to botanical arrangement, which
these nosologists profess to imitate, to call the distinct and confluent