oy 
PREFACE. 
Hye long meditated the commencement 
of a work on the medicinal vegetables of the 
United States, and feeling myself obligated for its 
completion, by the instructions from the Univer- 
sity in which I have the honor to hold a professor- 
ship; it may be proper to make at the outset some 
general statements of the motives and objects of 
such a publication. 
The Materia Medica, comprising the great 
body of medicinal agents now in use in the hands 
of physicians, cannot be said to need an increase 
in the number of its articles. It is already in- 
cumbered with many superfluous drugs; even its 
active substances are more numerous than can be 
of use to any one physician, so that it seems quite 
as susceptible of benefit from reduction as from 
augmentation in the number of its materials. 
Under these circumstances, the introduction of 
new medicines can only be authorized, where 
