A spot of this solution is mixed with the blood on a slide by means of a mounted needle, and covered with a clean cover-glass. The red corpuscles are slightly stained, while the nuclei of the white corpuscles are stained a bright crimson, and the “blood plates” a deep pink colour. Stained preparations may also be obtained by using *Toison’s fluid*, which serves also for diluting the blood in order to determine the exact number of red and white corpuscles present by means of Gowers’ or the Thoma-Zeiss hæmocytometer. It is prepared thus:-- Glycerine 30 c.c. 1 oz. Sodium sulphate 8 grms. 2 drms. Sodium chloride 1 grm. 15 grs. Methyl violet ·25 grm. 4 grs. Distilled water 160 c.c. 5 oz. It stains the nuclei and blood plates, but does not alter the shape of the red cells. It requires to be made up fresh occasionally as torulæ are apt to form and multiply in it. Dried films may be stained with hæmatoxyline, picrocarmine, or any of the general stains. The nuclei of the leucocytes may be stained rapidly in a couple of minutes in a one per cent. solution of methyl violet, washing in water, drying between blotting paper and mounting in balsam. The best method for general purposes is to stain with a saturated aqueous solution of methyl blue for half an hour or longer. Wash in water, and then stain for ten minutes in a half saturated aqueous solution of eosine. In this way the eosinophile granules of the leucocytes and the red corpuscles, are stained by the eosine, while the nuclei of the leucocytes are stained by the methyl blue. Kanthack and Drysdale recommend that the film should first be stained with a half per cent. solution of eosine in 50 per cent. alcohol, then washed, dried and fixed in the flame, and stained for a short time in Löffler’s solution of methylene blue (p. 104). These films may be stained for micro-organisms in the way described for cover-glass preparations (p. 112). CHAPTER VIII. INJECTION OF BLOOD VESSELS. Injection of blood vessels may be performed on small animals, or on individual human organs after removal from the body. The object is to fill the vessels with a coloured fluid which will solidify afterwards. It is possible in the same organ to inject the arteries with a red medium, the veins blue, and secretory ducts, such as bile ducts, yellow or blue. The most convenient basis for an injection mass is gelatine, as its solutions liquefy at a temperature of about 100° F., and solidify a little below that point, and when solidified cut readily, and do not tend to become brittle. The various masses are prepared as follows:-- *Red injection mass* (Woodhead’s formula) consists of gelatine softened by mixture with water and coloured by carmine. (1) Carmine 4 grms. Liq. ammoniæ B.P. 8 grms. Distilled water 150 c.c. Dissolve the carmine in the ammonia in a mortar. Pour on the water. Mix thoroughly and filter.