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. 1. GENERAL STIMULANTS. The four classes comprehended under this first division, are NARCOTICS, ANTISPASMODICS, TONICS, and ASTRINGENTS. Although these remedies differ very essentially in the degree and permanence of their action, as well as in the character of their apparent effects, yet, as it is conceived that their _primary_ operation is stimulant, they are considered as possessing sufficient general similitude to sanction their arrangement under one comprehensive division. NARCOTICS. Synon: _Sedatives._ _Anodynes._ _Hypnotics._ _Soporifics._ Substances which, in a moderate dose, occasion a temporary increase of the actions of the nervous and vascular systems, but which is followed by a greater depression of the vital powers than is commensurate with the degree of previous excitement, and which is generally followed by sleep.