Finally, corrosions are indispensable to the removal of the parenchyma from injected preparations, when it is intended only to preserve the interior network of vessels. The following are the attentions which this operation exacts: The injected part is consigned to a vessel of pure water for two or three days, which is occasionally to be renewed, in order the better to disgorge the vessels of any blood they may contain. It is afterwards to be solidly fixed on a piece of wax at the bottom of a porcelain vase, pierced with holes near the base, through which the liquor used to wash them may flow off without deranging the vessels. This corrosive liquor is the muriatic acid, or spirit of salt; the aquafortis of engravers, or nitric acid, may be used for the same purpose. The first time, the preparation is to remain two or three hours in this acid, which is then drawn off and replaced by the same quantity of water, which is allowed to flow on it in small streams. This water is left for four or five days, according to the season, until the water begins to be covered with a scum, and the preparation begins to be cottony at its surface; the liquor is poured off a second time, and the pot or vase is placed beneath the cock of a fountain, from which escapes a delicate stream of water, which will carry off slowly and without shocks, any detached parts; when it is perceived that the washing carries off no more animal matter, the acid is poured into the pot, of which the opening is to be reclosed with a stopper of glass or porcelain, warmed and endued with wax. This operation is to be repeated every four or eight days, until the tunics of the vessels are altogether denuded, and the injected matter is seen throughout.[9] [9] These details on maceration and corrosion, are extracted from a work full of interest of Professor Dumèril: Essay on the means of perfecting and extending the anatomical art.--(_Paris_, 1803.) _c._ _Injections._--These are _evacuative_, _repletive_, _antiseptic_, or _preservative_. The first have for object, as their name indicates, to disembarrass the vessels or hollow organs, of the matters and fluids which they contain; they consist of water, of acids very much reduced, of diluted alcohol, &c. Thus it is serviceable to inject water or alcohol into the bloodvessels to prepare them for the reception of the repletive and preserving injections. The second are either definite or temporary. The substances employed in these injections are vehicles for colouring matter. The nature of the vehicles determines that of the colours, which ought to be as far as possible, analogous to those of the humors, which the vessels contained during life. As vehicles, those fluids which always retain their fluidity are rarely employed, for parts thus injected cannot be dissected, and they are, besides, apt to allow the colouring matters which they contain in suspension, to be deposited.