- 
over the whole system, and quickly produces its full exci- 
: : z . . *, 
effect. A diffusible stimulus is generally also transient in its — 
; in other words, the effect, though soon produced, quick- 
es. There are others, on the contrary, which, though equally. 
ulants, are slow and permanent. These varieties, 
ficiently established, serve to explain the differences in 
of a number of the most important medicines; and they 
e foundation for the distinction of two great classes, narcotics 
d tonics, with their subordinate divisions of antispasmodics and 
ingents, both consisting of powerful stimulants : one diffusi- 
- ble and transient, the other slow and permanent in their operation. _ 
If. There is a difference between stimulants, in their actions be- 
ing directed to particular parts. Some, when received into the 
stomach, quickly act upon the general system; others have their 
___ action confined to the stomach itself, or, at least, any farther stimu- 
_ lant effect they may occasion is slow and inconsiderable ; while a 
ss Consists of those which operate on one part, often without 
sing any sensible effect on the stomach or general system. 
S act on the intestinal canal; others on the kidneys, blad- 
of the skin, and other parts; the affection they excite 
being the consequence, not of any stimulanf ation 
1 extended over every part, bat of ‘one tibke particu a se 
termined. This difference in the action of stimuli is the principal 
foundation of the distinctions of medicines into particular classes. 
Cathartics, for instance, are those medicines, which, as stimuli, act” 
peculiarly, on the intestinal canal : diuretics, those which act on the 
secreting vessels of the kidneys : emmenagogues, those which act 
the uterine system ; diaphoretics, those which exert a stimulant a 
on the vessels of the skin. With these operations, medicines, a 
Same time, act more or less as general stimulants, by which é 
lual pee ie to any class is thus rendered capable of 
effects 
aC U 
their effects 
termined to particular parts, are sometimes conveyed to these part 
in the course of the circulation ; more generally their action is e® 
tended from the stomach, or part to which they are applied, b 
These operatic 
extensive than 
e deduced 
of nges which the solids and fluids underwent in 
of this kind, 
tinetions fc 
These observ. 
