~Nutrose Agar (Eyre).~-- (This is a modification of the well known Drigalski-Conradi medium originally introduced for the isolation of B. typhosus). 1. Collect 250 c.c. perfectly fresh ox serum (_vide_ Blood Serum, page 168, steps 1 to 5) and add to it 450 c.c. sterile distilled water. 2. Weigh out agar powder, 20 grammes, and emulsify it with 250 c.c. of the cold serum water. 3. Weigh out Witté's peptone 10 grammes Sodium chloride 5 grammes Nutrose 10 grammes and dissolve in 200 c.c. of serum water heated to 80° C. 4. Mix the agar emulsion and the peptone-nutrose solution in a "tared" flask of 2-litre capacity and add a further 100 c.c. serum water. 5. Complete the solution of the various ingredients by bubbling live steam through the flask as in making nutrient agar. 6. Add further 250 c.c. serum water. 7. Weigh the flask and its contents: then (1045 grammes + weight of flask) minus (weight of flask and its present contents) = weight of fluid required to make up the bulk of the medium to 1 litre. Add the requisite amount of sterile distilled water. 8. Titrate and estimate the reaction of the medium mass. Then standardise to reaction of +2.5. 9. Clarify with egg, and filter as for nutrient agar. (In clarifying, after the addition of the egg white the mixture should be in the steamer for full two hours.) 10. After filtration is complete measure the filtrate, and to every 150 c.c. of the medium add: Litmus solution (Kahlbaum) 20 c.c. Krystal violet aqueous solution (1:1000) (B. Hoechst) 1.5 c.c. Lactose 1.5 grammes 11. Tube in quantities of 15 c.c. 12. Sterilise in the steamer at 100° C. for thirty minutes on each of three successive days--i. e., by the discontinuous method for three days. ~Egg Medium (Dorset).~-- 1. Prepare 1000 c.c. of a 0.85 per cent. solution of sodium chloride in a stout 2-litre flask. 2. Sterilise in the autoclave at 120° C. for twenty minutes. Cool to 20° C. 3. Take 12 fresh eggs; wash the shells first with water then with undiluted formalin: allow the shells to dry. 4. Break the eggs into a sterile graduated cylinder and measure the total volume of the mixed whites and yolks. Add one part sterile saline solution to three parts mixed eggs. 5. Transfer this mixture to a large wide-mouthed stoppered bottle previously sterilised. Add sterile glass beads and shake thoroughly in a mechanical shaker for about thirty minutes, or whip with an egg-whisk. 6. Filter through coarse butter muslin into a sterile flask. NOTE.--A few drops of alcoholic solution of basic fuchsin (sufficient to give a definite pink colour), or a few drops of waterproof Chinese ink added to the medium at this stage facilitates the subsequent "fishing" of colonies. 7. Tube in quantities of 10 c.c. 8. Solidify in the sloping position in the inspissator at 75° C. for one hour.