11. =Injection.= Injections for the demonstration of blood-vessels, lymphatics, ducts of glands, etc., are rarely used in pathologic work. The organs to be injected must be fresh, warm from the body, if possible. The vessels should be washed out by a freshly filtered 8 per cent sodium nitrate or sodium sulphate solution, followed by physiologic salt-solution. A cannula is introduced into a main vessel, tightly secured, and then connected with a syringe or a gravity injection-apparatus giving a constant pressure. The injection-mass is then injected under a low pressure. In the case of injections into lymphatic vessels the cannula should be introduced into the largest lymphatics at the periphery of the blood-vessels where larger lymph-vessels are more easily found. Injections are made with either cold or warm solutions; the latter are preferable but require that the organ to be injected be warmed by immersing it in water at a temperature of 40°C. The injection fluid must be of the same temperature. After the warm injection is given the organ is put into ice-cold 10 per cent formol solution until fixed and then after-hardened, imbedded and stained as desired. After the use of cold injections the tissues are fixed in 10 per cent formol, alcohol, or any other desired solution, and treated according to the end sought. Nuclear and diffuse stains contrasting with the color of the injection mass should be used. The process of injection requires great care; the pressure must be carefully regulated to prevent extravasations, and the injection-fluid must be free from air-bubbles. The injection is continued until the organ appears diffusely stained. Blood-vessels are fixed in their natural blood-injection by such agents as formol and chromic acid, so that stains acting upon the red blood cells cause the veins and capillaries to appear as if they had been injected. The following injection masses are advised:— 1. =Cold Injection Mass (Beale’s Glycerin Carmine):—= Dissolve 0.3 grm. of carmine in a small quantity of water containing 5 drops of ammonia; add 15 cc. of glycerin and shake; add drop by drop 15 cc. of glycerin containing 8-10 drops of glacial acetic acid. Then add further glycerin 15 cc., alcohol 8 cc., and water 24 cc. 2. =Warm Injection Mass (Thiersch’s Berlin-blue Gelatin):—= (_a_) Dissolve 1 part of gelatin in 2 parts of water by allowing it to soak 24 hours, and then warming. Filter through flannel. (_b_) Saturated water solution of ferrous sulphate. (_c_) Saturated water solution of red ferricyanide of potassium. (_d_) Saturated water solution of oxalic acid.