Penh BOTANIC PHYSICIAN. ——— 
~ neral resemblance in their virtues. But though indications of this 
kind may be partially true, they are extremely limited in their operae 
.tion, and are liable to many causes of obscurity and error. 
The cnemicat nistory of the articles of the materia medica, em> 
braces several important subjects of inquiry. 
r analysis, especially that of those belonging to the vegetable _ 
3 agdom, has been supposed capable of leading to a knowledge of | 
_ their virtues; and the opinion does not, at first thought, appear im- 
probable, since the medicinal powers of any compound body, in com= 
‘mon with its other internal properties, must arise from its peculiar 
composition. It may be remarked, however, that even from the re- 
searches of modern chemistry, little information of this kind can be _ 
acquired. It may be discovered, indeed, in what proximate princi- 
ple of any vegetable substance its virtues reside ; but this affords no 
previous indication of these virtues. Nor can the analysis of these 
principles explain the source of the powers which are attached to 
in particular substances ; the peculiarities of composition from _ 
these may originate, being by far too subtile to be detected by — 
al nreans. ial ae ; 
nistty, however, is in other respects more directly useful in 
ication to the materia medica. It enables us, by the use of 
proper solvents, or the due application of heat, to separate those 
proximate principles of vegetables in which their virtues reside, from 
other inert or noxious matter with which they may be mixed ; it as- 
a certains how far these processes are useful, points out those changes. * 
4m composition, by which the virtues of the substances acted om are 
frequently altered, and the means by which such injuries may be les- _ 
sened or prevented. Similar advantages are obtained from its-ap- 
plicatic the few products of the animal kingdom that are used in 
medi those which are derived from the mineral kingdom, — 
¢ plo. yed with advantage and discrimination only when their | 
composition is known; and the analyses of these substances have 
exploded many crrorssrespecting them, have enabled us to distin- 
guish them from each other, have pointed out the identity of others, 
and have rectified the processes by which they are prepared, 
By new combinations, chemistry furnishes us with many remedies 
equally active and important with those afforded by Nature ; and by ' 
peeing out the gaia chemical action of different substances, it 
. Guards against the errors which might arise from jmpranor mixe_ 
tures. . oes nnn ee Agi 
= The last object in the study of the materia medica, that to which 
he others are merely subservient, is the MEDICAL HIsToRY of its al- 
ticles ; the investigation of their 
the treatment of disease. - 
_ This includes, in the first place, the consideration of the action of 
these substances on the. system, in general, as this being ascertain-_ 
ed, leads to their application in the treatment of morbid affections, - 
° 
rage 
a ees 
se 
virtues, or their practical uses in 
