NOTE.--Different percentages of glycerine--from 4 per cent. to 8 per cent.--are used for special purposes. Five per cent. is that usually employed. ~Glycerinated Potato.~-- 1. Prepare ordinary potato wedges (_vide_ page 174, sections 1 to 4). 2. Soak the wedges in 25 per cent. solution of glycerine for fifteen minutes. 3. Moisten the cotton-wool pads at the bottom of the potato tubes with a 25 per cent. solution of glycerine. 4. Insert a wedge of potato in each tube and replug the tubes. 5. Sterilise in the steamer at 100° C. for twenty minutes on each of _five_ consecutive days. ~Animal Tissue Media (Frugoni).~-- 1. Take a number of sterile test-tubes 16 × 3 or 4 cm., plugged with cotton wool, and into each insert a 2 cm. length of stout glass tubing (about 1 cm. diameter); fill in glycerine (6 per cent.) bouillon to the upper level of the piece of glass tubing. Sterilise in the steamer at 100° C. for twenty minutes on each of three successive days. 2. Kill a small rabbit by means of chloroform vapour. 3. Under strictly aseptic precautions remove the lungs, liver and other solid organs and transfer them to a sterile double glass dish. 4. With the help of sterile scissors and forceps divide the organs into roughly rectangular blocks 3 × 1.5 × 1 cm. 5. Pour into the dish a sufficient quantity of sterile glycerine solution (6 per cent. in normal saline), cover, and allow to stand for one hour. 6. Introduce a block of tissue into each tube so that it rests upon the upper end of the piece of glass tubing. (The surface of the tissue will now be kept moist by capillary attraction and condensation). 7. Sterilise in the autoclave at 120° C. for thirty minutes. 8. Cap the tubes and store them in the ice chest for future use. Tissues obtained at postmortems can also be used after preliminary sterilisation by boiling or autoclaving. _Media for the Study of Special Cocci._ _Diplococcus Gonorrhoeæ._ ~Ascitic Bouillon (Serum Bouillon).~-- 1. Collect ascitic fluid (pleuritic fluid, hydrocele fluid, etc.), by aspiration directly into sterile flasks, under strictly aseptic precautions. 2. Mix the serum with twice its bulk of sterile nutrient bouillon (_vide_ page 163). 3. If considered necessary (on account of the presence of blood, crystals, etc.), filter the serum bouillon through porcelain filter candle. 4. Tube, and sterilise in the water bath at 56° C. for half an hour on each of five consecutive days. 5. Incubate at 37° C. for forty-eight hours and eliminate contaminated tubes. Store the remainder for future use. ~Serum Agar (Heiman).~-- 1. Prepare nutrient agar (_vide_ page 167), to following formula: Agar 2.0 per cent. Peptone 1.5 per cent. Salt 0.5 per cent. Meat extract _quantum sufficit._ 2. Make reaction of medium + 10. 3. Filter; tube in quantities of 6 c.c. 4. Sterilise as for nutrient agar.