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]
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.
Liquids saturated with glue or gelatine, made use of in ordinary injections, have the inconvenience of not being equally solidifiable at different degrees of temperature, or harden too rapidly by cooling; they are made with the glue of commerce, either simple, or mixed with gummy or saccharine matter; that commonly used, is called Flanders glue, although it is manufactured in Paris, and that called mouth glue, which only differs from the other in containing a little gum or sugar. That which succeeds best, because it melts with the heat of the hand, and which nevertheless coagulates at a temperature of twenty-five or twenty-six degrees of Reaumer’s thermometer, which is one of the highest points to which our atmosphere attains, is made of the membranes of fishes, or icthyocolla. An ounce is to be melted in a sand-bath, in double its weight of water, and mixed afterwards with two ounces of alcohol, previously warmed. In these sorts of gelatinous injections, there is much choice in the colouring matters. All those that are ground like gum, and which are used in miniature painting, and in painting “a la gouache,”[M] may be employed; they remain very well suspended.
The sticks of carmine of Delafosse, and the carmine lacks of Hubert, may then be used with advantage for the arteries; for the veins, Prussian blue, ground in vinegar, and the white of zinc of Antheaume, or that of oyster shells well porphyrized, for the colour of metallic oxide is subject to change in animal matter; they are also subject to the inconvenience of becoming precipitated by repose before the vehicle cools, and thus obstruct the smaller vessels.
Liquors which can be made solid by the effect of certain re-actives, offer, on this account, some advantage. It is thus, that it is serviceable to soak for a day or two in a solution of nut-galls or of tannin, those parts injected with gelatine, when it is intended to preserve them dry. In partial injections of lymphatic vessels, and particularly of the chyliferous, cow’s or goat’s milk, may be made use of. When, after having tied the thoracic duct, injections of milk have been made into all the vessels in which can be introduced the beak of a glass syringe, or of the syringe used for injecting the lacrymal ducts, pour on the surface of the injected parts strong vinegar, or a diluted acid, which will coagulate the milk, so that the chyliferous vessels will be found filled with a solid, white, and flexible.[10]
The most common, the most solid, and the most convenient injections, are made of fatty and resinous matter. Volatile oils, balsams, resins dissolved in alcohol, fats, wax, and the most ordinary fixed oils, are principally used. These different substances are combined, and the compositions of them are varied according to the nature of the injections, which it is desirable to prepare, and above all, according to the manner which it is proposed to preserve them.
The nature and the preparation of the colouring matters, ought also to vary according to the kind of fatty medium which is used.