_A._ GENERAL STIMULANTS.
a. _Diffusible._ { _Narcotics._
„ { _Antispasmodics._
b. _Permanent._ { _Tonics._
„ { _Astringents._
_B._ LOCAL STIMULANTS.
_Emetics._
_Cathartics._
_Emmenagogues._
_Diuretics._
_Diaphoretics._
_Expectorants._
_Sialogogues._
_Errhines._
_Epispastics._
_C._ CHEMICAL REMEDIES.
_Refrigerants._
_Antacids._
_Lithontriptics._
_Escharotics._
_D._ MECHANICAL REMEDIES.
_Anthelmintics._
_Demulcents._
_Diluents._
_Emollients._
With respect to the classification of Dr. Cullen, we may commence our
objections by stating, that the very basis upon which it rests is a mere
gratuitous assumption, viz. _that certain medicines act on the fluids of
the body_. With the exception of a very few substances, it is now
generally admitted that medicines produce their effects by acting on the
living materials of which our organs are composed, and not by modifying
the specific gravity, or chemical composition, of the fluids which they
may happen to evacuate. The origin of this latter opinion is to be
traced to the exploded notions of the humoral pathologists, and to the
exclusive doctrine of the earlier chemists; for as the former recognised
a depraved condition of the fluids as the source of every disease, so
did the latter imagine that every remedy operated by producing a
chemical change upon its composition; and the remedial value of a
medicinal substance was estimated by its effects upon inert matter. Thus
were experiments made with different substances upon the blood, and
other fluids of the body, in order to deduce, from the results, the
nature and extent of their powers as agents upon the living frame; for
instance, the _spirit_ and _salt of hartshorn_, as they were found to
render the blood more fluid, when added to it, _out of the body_, were
indiscriminately administered in almost every complaint, with a view to
dissolve that “lentor of the fluids” which was regarded as the more
general source of disease. For similar reasons, a tribe of medicines
were introduced into practice under the title of _Antiseptics_, for the
prevention of a process which very probably never takes place in the
living body: the powers of these supposed agents were, as usual,
inferred from their effects in resisting and preventing the putrefaction
of dead matter.
Nor is the distinction assumed by Dr. Cullen, between the action of
remedies on the _Simple_ and _Living_ solids less hypothetical. Tonics
and astringents may certainly exert a beneficial effect upon the animal
fibre, but not by any immediate action on its materials, but through the
agency of its living principle.—“_Medicamentum non agit in cadaver._”
The classification of Dr. Young, although it presents many points of
interest and value, is not altogether free from objection; his classes
in some instances are perhaps unnecessarily sub-divided, without a
sufficient regard to the primary and secondary operations of the
substances which they include. The arrangement of Murray has been
adopted in the present inquiry, not as being less objectionable, in a
general point of view, but as one which from its simplicity, is better
calculated, as a frame-work, if I may so express myself, for the display
of those particular facts, the knowledge of which I consider essential
for the successful administration of medicinal agents, and for the full
comprehension of those practical doctrines which it is the exclusive
object of this work to inculcate.
Dr. Murray observes that, in this arrangement, he places in the first
division those substances which exert a GENERAL STIMULANT operation on
the system. Of this there are two sub-divisions, the DIFFUSIBLE and the
PERMANENT; the former including the class of _Narcotics_, with which may
be associated, as not very remote in their operation, the class of
_Antispasmodics_; the latter comprising two classes, viz. _Tonics and
Astringents_. Through these there is a gradual transition from the most
highly diffusible stimulant, to those most slow and durable in their
action.
A second division comprehends LOCAL STIMULANTS, those, the action of
which is determined to particular parts of the system. Such are the
classes of _Emetics_, _Cathartics_, _Emmenagogues_, _Diuretics_,
_Diaphoretics_, _Expectorants_, and _Sialogogues_; with which may be
associated the classes of _Errhines_ and of _Epispastics_, founded on
direct local application.
The remaining classes include substances which do not operate according
to laws peculiar to the living system. To one division may be referred
those, whose effects depend on the CHEMICAL changes they produce in the
fluids or solids; the classes which may be established on this principle
are _Refrigerants_, _Antacids_, _Lithonthriptics_, and _Escharotics_. To
another division belong those, the operation of which is purely
MECHANICAL, as _Anthelmintics_, _Demulcents_, _Diluents_, _Emollients_,
and certain _Laxatives_.
Under the above classes, says Dr. Murray,[137] may be comprehended all
those substances which are capable of producing salutary changes in the
human system, and which are used as remedies. I have stated my reasons
for adopting this as a general basis of classification, although I shall
deviate very considerably in the subordinate divisions of the plan, in
the hope of establishing some distinctions that may tend to practical
utility.