7. Control the result of these experiments. Dry--Spores: The thermal death-point in this case is that ~temperature~ which with certainty kills the spores of the organism in question when present in a thin film after a time exposure of ~10 minutes~. _Apparatus Required:_ As for vegetative forms. METHOD.-- 1. Prepare a sloped agar tube cultivation and incubate under optimum conditions as to spore formations. 2. Pipette 5 c.c. sterile normal saline into the culture tube and emulsify the entire surface growth in it. Examine microscopically to determine the presence of spores in large numbers. 3. Spread thin even films on twelve sterile cover-slips and place each cover-slip in a separate sterile capsule. 4. Expose each capsule in turn for ten minutes to a different fixed temperature, varying 5°C, between 100° C. and 160°C. 5. Complete the examination as for vegetative forms. ~III. Reaction of Medium.~ (A) _Range._-- 1. Prepare a bouillon culture of the organism and incubate, under optimum conditions as to temperature and atmosphere, for twenty-four hours. 2. Pipette 0.1 c.c. of the cultivation into a sterile capsule; add 9.9 c.c. sterile bouillon and mix thoroughly. 3. Prepare a series of tubes of nutrient bouillon of varying reactions, from +25 to -30 (_vide_ page 155), viz.: +25, +20, +15, +10, +5, neutral, -5, -10, -15, -20, -25, -30. 4. Inoculate each of the bouillon tubes with 0.1 c.c. of the diluted cultivation by means of a sterile graduated pipette and incubate under optimum conditions. 5. Observe the cultures at half-hourly intervals from the third to the twelfth hours. Note the reaction of the tube or tubes in which growth is first visible macroscopically (probably optimum reaction). 6. Continue the incubation until the completion, if necessary, of seven days. Note the extremes of acidity and alkalinity in which macroscopical growth has developed (Range of reaction). 7. Control the result of these observations. (B) _Optimum Reaction._--The optimum reaction has already been roughly determined whilst observing the range. It can be fixed within narrower limits by inoculating in a similar manner a series of tubes of bouillon which represent smaller variations in reaction than those previously employed (say, 1 instead of 5) for five points on either side of the previously observed optimum. For example, the optimum reaction observed in the set of experiments to determine the range was +10. Now plant tubes having reactions of +15, +14, +13, +12, +11, +10, +9, +8, +7, + 6, +5, and observe as before. ~IV. Resistance to Lethal Agents.~-- (A) _Desiccation._-- _Apparatus Required:_