ride 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.

5. Examine each of the culture tubes from day to day, until the
completion of seven days, and note those tubes, if any, in which growth
takes place.

6. From such tubes as show growth prepare subcultivations upon suitable
media, and ascertain that the organism causing the growth is the one
originally employed in the test and not an acc