Fig. 241.—Injecting Syringe.
Fig. 242.—Water Bath and Melting Vessels.
The injection of animal bodies practised by the older anatomists, to render the vascular system more apparent, has not been superseded by the more modern methods of staining. The method of injecting even small bodies requires some skill, and a few pieces of apparatus made expressly for the purpose. First, a special form of brass syringe of such a size that it may be grasped with the right hand, the thumb at the same time covering the button at the top of the piston-rod when drawn out to the full. In [Fig. 241] the piston rod is seen withdrawn, a is the body, with a screw at the top for firmly screwing down the cover, b, after the piston, c, is replaced; e is a stop-cock, to the end of which either of the smaller cannulæ, g, is affixed. The transverse wires are for securing them tightly with thread to the vessels into which they are to be inserted. In addition to the syringe, two or three tinned vessels are required to contain size, injecting fluid, and hot water.
The size must be kept hot by the aid of a water bath; if a naked fire be used there is danger of burning it. A convenient form of apparatus for melting the size, and afterwards keeping it at a proper temperature, is [Fig. 242].
Fig. 243.—Artery Needle.
A pair of strong forceps for seizing the vessel, and a small needle ([Fig. 243]) is also necessary for passing the thread round the vessel into which the injection pipe has been inserted. These complete the list of apparatus. To prepare the material for opaque injections, take one pound of the finest and most transparent glue, break it into small pieces, put it into an earthen pot, and pour on it three pints of cold water; let it stand twenty-four hours, stirring it now and then with a stick; set it over a slow fire for half an hour, or until all the pieces are perfectly dissolved, skim off the froth from the surface, and strain through a flannel for use. Isinglass and cuttings of parchment make an excellent size, and are preferable for particular injections. If gelatine be employed an ounce to a pint of water will be sufficiently strong, but in very hot weather it is necessary to add a little more gelatine. It must be first soaked in part of the cold water until it swells up and becomes soft, when the rest of the water, made hot, is to be added. The size thus prepared may be fixed with finely levigated vermilion, chrome-yellow, blue salts, or flake white.
To prepare the subject, the principal points to be attained are: to dissolve the fluids and completely empty the vessels; relax the solids; and prevent the injection from coagulating too soon. For this purpose it is necessary to place the animal, or part to be injected, in warm water, as hot as the operator’s hand will bear. This should be kept at nearly the same temperature for some time by occasionally adding hot water. The length of time required is in proportion to the size of the part and the amount of its rigidity.