4. Add the nutrose ascitic solution to the fluid agar. 5. Heat in the steamer for thirty minutes, then filter. 6. Tube and sterilise as for nutrient agar. NOTE.--The finished medium in this case measures 900 c.c. only since inconvenient fractions would be introduced in making up to one litre exactly. _Diplococcus Pneumoniæ._ ~Blood Agar (Washbourn).~-- 1. Melt up several tubes of nutrient agar (_vide_ page 167) and allow them to solidify in the oblique position. 2. Place the tubes, in the horizontal position, in the "hot" incubator for forty-eight hours, to evaporate off some of the condensation water. 3. Kill a small rabbit with chloroform and nail it out on a board (as for a necropsy). Moisten the hair thoroughly with 2 per cent. solution of lysol. 4. Sterilise several pairs of forceps, scissors, etc., by boiling. 5. Reflect the skin over the thorax with sterile instruments. 6. Open the thoracic cavity by the aid of a fresh set of sterile instruments. 7. Open the pericardium with another set of sterile instruments. 8. Sear the surface of the left ventricle with a red-hot iron and remove fluid blood from the heart by means of sterile pipettes (e. g., those shown in Fig. 13, c). 9. Deliver a small quantity of the blood on the slanted surface of the agar in each of the tubes, and allow it to run over the entire surface of the medium. 10. Place the tubes in the slanting position and allow the blood to coagulate. 11. Return the "blood agar" to the hot incubator for forty-eight hours and eliminate any contaminated tubes. Store the remainder for future use. _Media for the Study of Mouth Bacteria Generally._ ~Potato Gelatine (Goadby).~-- 1. Prepare glycerine potato broth (see page 203, sections 1 to 5). 2. Add 10 per cent. gelatine to the potato decoction and bubble live steam through the mixture for ten minutes. 3. Estimate the reaction; adjust the reaction of the medium to +5. 4. Cool the medium to below 60°C., clarify with egg as for nutrient gelatine. 5. Filter through papier Chardin. 6. Tube, and sterilise as for nutrient gelatine. _Media for the Study of Protozoa._ ~Tissue Medium (Noguchi).~--_For spirochætes (cultivations must be grown anaerobically)._ 1. Plug and sterilise test-tubes 20 × 2 cm. 2. Kill a small rabbit with chloroform vapour. Open the abdomen with all aseptic precautions, remove kidneys and testicles and transfer to a sterile glass dish. Cut up the organs with sterile scissors into small pieces--say 4 millimetre cubes. The four organs should yield from 25 to 30 pieces of tissue. 3. Drop a small piece of sterile tissue into the bottom of each sterilised tube. 4. Take a flask containing about 400 c.c. nutrient agar (+10 reaction), liquefy the medium by heat and cool in a water bath to 50°C. 5. Add 200 c.c. ascitic or hydrocele fluid (horse or sheep serum may be employed, but is not so good) to the liquid agar and mix carefully to avoid formation of air bubbles.