19 
seen to exist in the vegetable kingdom. But if we look at 
the different kinds of animals employed as food, and those 
which are not so, we shall see a recognition of the principle; 
as well as in the employment of several species of the tribe 
of Cantharidia, as vesicatories in different countries. 
From viewing the Organic we proceed to the Inorganic 
kingdom of nature, and Mineralogy, as one great division 
of natural history, embraces within its consideration the 
structure and relations of minerals, or all bodies found in 
or upon the earth, which are neither animal nor vegetable. 
Crystallography is a branch of this science, which describes 
and explains the relations that subsist among the crystal- 
line forms of minerals, while Geology makes us acquainted 
with the structure, relative position, materials, and mode 
of formation of the mineral masses, of which the crust of 
the earth is composed. Minerals, though inorganized, act 
on organized matter, so as to produce those changes in its 
state and functions, which make them useful as medicines. 
They may, whether solid, liquid, or aeriform, be arranged 
and distinguished, either according to their physical charac- 
ters, or their chemical composition. But few are now 
employed, either as external or internal remedies, until 
they have been subjected to some chemical operation, 
either to improve their quality, or to change their nature. 
As all that are employed as medicines are also objects 
of chemistry, it is in every way preferable to treat of 
them according to the most approved arrangements of this 
science ; introducing, however, in appropriate places, the 
natural history and physical characters of such as are 
chiefly the produce of nature. It is indispensable, therefore, 
that we be acquainted with the sciences which treat of 
them in this view, to know that we use their terms with 
propriety and correctness. 
But these studies, extensive though they be, and indispen- 
d 2 
