Injecting the systems of Vessels with different colours: Carmine and Gelatine Injection.—Carmine 30 grains, strong liquid ammonia 60 drops, glacial acetic acid 43 drops, gelatine solution (one ounce in six ounces of water) two ounces, water one ounce: dissolve the carmine in the ammonia and water in a test tube, and mix it with one half of the warm gelatine, add the acid to the remaining half of gelatine, and drop it little by little into the carmine mixture, stirring it well with a glass rod during the mixing; filter through flannel, and add a few drops of carbolic acid to make it keep. It is very important that the stain should be quite neutral, the test of which is the colour and smell of the fluid. It should be a bright red, and all trace of smell of ammonia must be removed.
Prussian or Berlin Blue and Gelatine.—Take 1½ ounces of gelatine, place it in a vessel and cover it with water; allow it to stand until all the water is absorbed and the gelatine is quite soft, then dissolve in hot water. Dissolve one drachm (60 grains) of Prussian or Berlin blue in six ounces of water, and gradually mix it with the gelatine solution, stirring well with a glass rod during the mixing; then filter as before.
Watery Solution of Berlin Blue.—Dissolve 2½ drachms of the blue in 18 ounces of distilled water, and filter. This staining fluid is used for injecting the lymphatic system.
Directions for Injecting.—The animal to be injected must be first killed by chloroform, and injected while still warm; to secure this place the body in a water bath, at a temperature of 104° Fahrenheit. Expose the main artery of the parts to be injected, clear a small portion of it from the surrounding tissues, and place a ligature of thin tissue or silk round it, by means of the small artery needle ([Fig. 243]). With a pair of sharp-pointed scissors make an oblique slit in the wall of the vessel, insert the cannula, and tie the ligature firmly over the artery behind the point of the cannula, into which put the stop-cock. Fill the syringe with injection fluid, which must not be too warm, and take care not to draw up any air-bubbles; insert the nozzle of the syringe into the stop-cock and force in a little fluid; remove the syringe so that the air may escape, re-insert the syringe, repeat the process until no air-bubbles escape, and then proceed slowly with the injection. Half an hour will be required to complete the process in an animal the size of a rabbit. To judge of the completeness of the injection, examine the vascular parts of the lips, tongues and eyes; if satisfactory, tie the ligature round the artery and withdraw the syringe; place the animal in cold water for an hour to consolidate the injection fluid. When cold dissect out the organs, cut them up, and place them in methylated spirit to harden. Change the spirit every twenty-four hours for the first three days. The hardening process will be complete in ten days.
To inject lymphatics by the puncture process, a small-sized subcutaneous syringe should be used, filled with a watery solution of the prepared stains. Thrust the nozzle into the pad of the foot, (or tongue), and then rub the limb to cause the injection fluid to flow along the lymphatic vessels into the glands.
When the blue stain is used add a few drops of acetic acid to the spirit while the hardening process is going on.
Of Injecting Different Systems of Vessels with Different Colours.—It is often desirable to inject different systems of vessels distributed to a part with different colours, in order to ascertain the arrangement of each set of vessels and their relation to each other. A portion of the gall-bladder in which the veins have been injected with white lead, and the arteries with vermilion, forms an attractive preparation. Each artery, even to its smallest branches, is seen to be accompanied by two small veins, one lying on either side of it. By this method four different sets of tubes have been injected—the artery with vermilion, the portal vein with white lead, the duct with Prussian blue, and the hepatic vein with lake. There are also opaque colouring matters which may be employed for double injections.
Injecting the Lower Animals.—The vessels of fishes are exceedingly tender, and require great caution in filling them. It is often difficult or quite impossible to tie the pipe in the vessel of a fish, and it will generally be found a much easier process to cut off the tail of the fish, and put the pipe into the divided vessel which lies immediately beneath the spinal column. In this simple manner beautiful injections of fish may be made.
Mollusca (slug, snail, oyster, &c.).—The tenuity of the vessels of the mollusc often renders it impossible to tie the pipe in the usual manner. The capillaries are, however, usually very large, so that the injection runs very readily. In different parts of the bodies of these animals are numerous lacunæ or spaces, which communicate directly with the vessels. Now, if an opening be made through the integument of the muscular foot of the animal, a pipe may be inserted, and thus the vessels may be injected from these lacunæ with comparative facility.
Insects.—Injections of insects may be made by forcing the injection into the general abdominal cavity, when it passes into the dorsal vessel and is afterwards distributed throughout the system. The superfluous injection is then washed away, and such parts of the body as may be required removed for examination.