PREFACE. xi 
Emetine, as separated by Pelletier and Magen- 
die, is powerfully emetic. 
Morphium, obtained by Serturner, is a yery 
strong narcotic. 
The foregoing are some of the examples, which 
the present state of Chemistry allows us to ob- 
serve of affinity between chemical and medicinal 
characters. With a few exceptions they will be 
found to be strictly true. Yet the analysis of vege- 
tables is at present but imperfectly known, and an 
extended investigation is continually bringing new 
principles tolight. We can hardly expect that the 
business of generalization should be attempted 
with complete success, until the constituent facts 
are better understood. From what we already 
know, however, it is not chimerical to predict, 
that if the chemistry of vegetables were as per- 
fectly known in all its parts, as in those which we 
have detailed; their medicinal properties might 
be inferred, with at least as great certainty, as 
that which now attends most inferences in the 
conjectural science of medicine. 
In regard to the botanical affinities of plants, 
as affording evidence of their medicinal powers, 
much has been said and written. Petiver, Hoff- 
man, Linneus, Hasselquist, and recently the 
learned Professor Decandolle have bestowed much 
