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-
