(A) ~Inhibition coefficient~--i. e., that _percentage of the disinfectant_ present in the nutrient medium which is sufficient to prevent the growth and multiplication of the bacterium. (B) ~Inferior lethal coefficient~--i. e., the _time exposure_ necessary to kill _vegetative forms_ of the bacterium suspended in water at 20° to 25° C, in which the disinfectant is present in _medium_ concentration (concentration insufficient to cause plasmolysis). And if the bacterium is one which forms spores, (C) ~Superior lethal coefficient~--i. e., the _time exposure_ necessary to kill the _spores_ of the bacterium under conditions similar to those obtaining in B. The example here detailed only specifically refers to certain of the disinfectants: viz:--Bichloride of mercury; Formaldehyde; Carbolic acid; investigated with regard to B. anthracis, but the technique is practically similar for all other chemical disinfectants. ~Inhibition Coefficient.~-- _Apparatus Required:_ Case of sterile pipettes, 10 c.c. (in tenths). Case of sterile pipettes, 1 c.c. (in tenths). Sterile tubes or capsules for dilutions. Tubes of nutrient bouillon each containing a measured 10 c.c. of medium. Twenty-four-hour-old agar culture of a recently isolated B. Anthracis. _Germicides:_ 1. Five per cent. aqueous solution of carbolic acid. 2. One per cent. aqueous solution of perchloride of mercury. 3. One-tenth per cent. aqueous solution of formaldehyde. METHOD.-- 1. Number six bouillon tubes consecutively 1 to 6. Inoculate each from the stock cultivation of B. anthracis and at once add varying quantities[10] of the carbolic acid solution, viz.: To tube 1 add 2.0 c.c. (= 1:100) To tube 2 add 1.0 c.c. (= 1:200) To tube 3 add 0.6 c.c. (= 1:300) To tube 4 add 0.5 c.c. (= 1:400) To tube 5 add 0.4 c.c. (= 1:500) To tube 6 add 0.2 c.c. (= 1:1,000) 2. Prepare a similar series of tube cultivations numbered consecutively 7 to 12 and add varying quantities of the mercuric perchloride solution, viz.: To tube 7 add 0.1 (= 1:1,000) To tube 8 add 0.05 (= 1:2,000) To tube 9 add 0.03 (= 1:3,000) To tube 10 add 0.025 (= 1:4,000) To tube 11 add 0.02 (= 1:5,000) To tube 12 add 0.01 (= 1:10,000) 3. Prepare a similar series of tube cultivations numbered consecutively 13 to 18 and add varying quantities of the formaldehyde solution, viz.: To tube No. 13 add 1.0 c.c. (= 1:1,000) To tube No. 14 add 0.4 c.c. (= 1:2,500) To tube No. 15 add 0.2 c.c. (= 1:5,000) To tube No. 16 add 0.1 c.c. (= 1:10,000) To tube No. 17 add 0.075 c.c. (= 1:15,000) To tube No. 18 add 0.05 c.c. (= 1:20,000) 4. Incubate all three sets of cultivations under optimum conditions as to temperature and atmosphere.