Thus neither the primary nor the secondary subdivisions of this arrangement can be reasonably maintained in theory, and we must fall back on the ultimate groups which are based upon common experience. From this failure we may infer that the idea that medicines differ prominently in causing or diminishing vital activity, upon which idea this and many other arrangements are founded, is in fact an erroneous one. There is no such universal distinction. A medicine which at one time raises or excites the vital forces, may at another time depress them; it may do one thing with a sick man, the other thing with a healthy man; it may have the one effect when taken for a short time in moderation, the other effect when taken for a long time or in excess. In fine, the result of the operation of a medicine does not necessarily depend upon this alternative. Although there are undoubtedly some medicines which tend to stimulate the nervous forces, and others which tend to depress them, yet as there are many remedies which may operate well without doing either the one or the other, and whose operation does not depend at all upon this, the distinction cannot be generally applied. The next arrangement, that of Dr. Duncan, appears, as far as it extends, to be correct in theory. If some additions were made to it, it would be a tolerably perfect classification of this kind. Assuming as a basis the ultimate or practical effect of medicines, we may proceed to divide them into groups in a natural way. Food and liquids are of use in the nutrition of the tissues, and will form the first class. A second set of substances act so as to expel from the body certain humours and secretions. Another class exalt the tone of the nervous system, and through it stimulate the system at large. A fourth set depress the same. And a fifth group do none of these things; but their action results in certain obvious changes in the chemical nature of the secretions. DR. DUNCAN. ALIMENTA. Diluentia, Demulcentia. EVACUANTIA. Diaphoretica, Errhina, Expectorantia, Cathartica, etc. STIMULANTIA. Topica (irritants, etc.) Generalia permanentia. Generalia transitoria. DEPRIMENTIA. Refrigerantia, Narcotica. CHEMICA. Acida, Alkalina.