including likewise two classes, tonics and astringents. In thes 
there is a gradual transition passing into the one from the oth 
from the most diffusible and least durable stimulus, to the one most 
effects are in general to be ascribed, not to any operation exerted 
After these, those few medicines may be considered whose action 
is merely mechanical or chemical. To the former belong diluents, 
demulcents, and emollients. Anthelmintics may perhaps be refer- 
red with propriety to the same division. To the latter, or those 
at batgnpargrer: oneare antacids or absorbents, lithon 
Under ttessishaaigs may be comprehended all those substances 
capable of producing salutary changes in the human system. Seve- 
ral classes are indeed excluded which have sometimes been admit- 
ted ; but these have been rejected, either as not being sufficiently 
precise or comprehensive, or as being established only on erro- 
neous theory. oF Te 
The subdivisions of these classe$ may sometimes be established 
on the natural affinities existing among the substances arranged un- 
der each ; on their chemical cémposition ; their resemblance in sen- 
sible qualities ; or, lastly, on distinctions in their medicinal virtues 
more minute than those which form the characters of the class. In 
rent classes one of these methods will frequently be found pre- — 
ferable to any of the others. 
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= = - 
TABLE OF CLASSIFICATION. 
a 
Narcotics. 
Antispasmodics.. © 
Tonics. 
the latter, 
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