Of remedies composed of vegetable tonics, the useful application of this principle is also apparent. Thus the addition of _alkalies_, or _lime-water_, to the infusions of _Gentian_, &c. or to the decoctions of _Bark_, by rendering their extractive and resinous principles more soluble, increase their elegance, and exalt their virtues, (_Form. 39, 41_,) although this law admits of an important exception to be hereafter explained. A knowledge of this principle likewise offers many useful hints connected with the successful exhibition of active remedies; it points out the medicines which require dilution in order to promote their operation, and those whose too speedy and violent effects may be retarded and checked by an abstinence from all potation. Thus, in the exhibition of _Diuretics_ likely to become cathartic or diaphoretic, no liquid should be given for at least an hour after their administration; the same caution applies with respect to the _Compound Powder of Ipecacuan_, which has a strong tendency to excite vomiting. When the remedy has passed out of the stomach, then the ingestion of fluids may, and ought to be encouraged. To Sir Francis Milman the profession is highly indebted for hints concerning the importance of accompanying the exhibition of _Diuretics_ with plentiful dilution,[269] the arguments he adduces elucidate in a very satisfactory manner the view which has been just taken of the INFLUENCE OF SOLUBILITY. The influence of solubility[270] in increasing the virulence of a poisonous substance, has already been illustrated very fully (_page 135_,) and it has also been shewn under what circumstance it may be admissible. When these active substances are administered as remedies, in small doses, the precept respecting their solubility is even more important, for in such cases the smallness of the quantity places their operation more immediately under the control of various incidental agents; _destroy_ the solubility of a medicine, and you will probably divest it of those properties which render it useful. _Nitrate of Silver_, by coming in contact with a _Muriatic Salt_, is rendered quite inert, and may be discovered unaltered in the fæces of persons to whom it has been administered. See _Argenti Nitras_. Under the article _Plumbi Acetas_ the practitioner will also find that the conjunction of this substance with any sulphuric salt, at once deprives it of its valuable properties as a remedy in _Hæmopthysis_.