ON THERAPEUTICS. 
131 
some metals, as sulphates of copper, iron, and zinc; sesqui- 
carbonate of iron, combinations of iodine with copper and iron, 
and salts of barium, with arsenic or some of its compounds. 
Vegetable tonics are quinine and its combinations, the various 
barks containing bitter principles, gentian, quassia, and other 
preparations of plants possessing the bitter extractive matter. 
The modus operandi of these drugs is not easy to define; we 
can only assert, as an ultimate fact, that mineral acids have 
the property of improving the tone and healthiness of the 
textures. Chemically, they exert a certain antiseptic power, 
and retard or prevent the decay of organic matters ; probably 
this same property determines the extent of their tonic in¬ 
fluence. The metallic base would seem, also, particularly in 
the case of iron salts, to produce some tonic effect. The ad¬ 
mixture, however, of the acid and oxide of the metal, places 
the two in the most convenient state for introduction into the 
system, as the caustic properties of the acid are modified, 
and the insoluble base is usually rendered soluble. Vegetable 
tonics owe their tonic properties to their bitter and astringent 
principles. Their effects are less energetic than those of the 
mineral class, and they occasion much less disturbance in the 
organism ; for these reasons they are valuable in many slight 
cases of debility, where the more powerful mineral agent 
would be unnecessarv. 
•f 
The tonic system of treatment may be pursued with two 
distinct intentions. First, it may be an object to improve the 
digestive and general secretive functions, that have been 
impaired from the various causes which we have mentioned, 
viz., the insufficient supply of food, or too much exertion, or 
the effects of an acute disease. Animals subjected to any 
debilitating influence for a long time suffer a diminution of 
vital energy, which a simple change of management, absolutely 
necessary as it is, may not suffice to restore. The functions 
are so far disordered that a purer atmosphere, better food, 
and properly proportioned exercise, are not enough to effect 
all that is required, principally on account of the derange¬ 
ment of the digestive svstem preventing the assimilation of 
nutriment, and so frustrating the beneficial effects that might 
otherwise be expected from the change. In such instances, 
a complete alteration of diet will sometimes produce mar¬ 
vellously satisfactory results. A complete change of food, 
however easy in human medicine, is sometimes impossible 
in the lower animals, whose dietary is so simple and 
limited. Medicinal aid will therefore be necessary to effect a 
permanent improvement. Tonics, properly applied, with the 
view to assist the dietetic treatment, not with the idea that 
