Chapter XVI: Appendix: 492 (14)

2. Pipette into each 5 c.c. respectively of the five percentage solutions of x-disinfectant which the trial run has already shown will include those affording lethal values at 2-1/2 and 30 minutes.

3. Arrange 20 tubes of bile salt broth in the upper tier of the test-tube rack in two rows, those in the front row numbered consecutively from left to right 1-10, those in the back row 11-20.

4. Arrange further 20 tubes of bile salt broth numbered 21-40 in two rows in a second smaller rack which can be stood on the upper tier of the rack as soon as the first 20 tubes have been inoculated.

5. Place a square wire basket of about 50 tube capacity close to the left of the test-tube rack, for the reception of the inoculated tubes.

6. Adjust a sterile 1 c.c. pipette in the mouth of each of the tubes, A, B, C, D and E, by means of a washer, as previously described.

7. Set the electric signal clock to ring for the commencement of the experiment and subsequently at 2-1/2, 5, 10, 15, 20, 25, 30 and 35 minutes.

8. Complete precisely as indicated in Trial Runs, steps 9-19.

_Control Phenol._--

Immediately the subculture tube from the 30-minute contact period have been inoculated, carry out a precisely similar experiment, in which five percentage strengths of Phenol, (e. g., 1.1, 1.0, 0.9, 0.75, 0.7) are arranged in the lower tier of the test-tube rack in place of the five strengths of Germicide-x.

Calculate the phenol coefficient by the following method:

(a) Divide the figure representing the percentage strength of the weakest lethal dilution of the carbolic acid control at the 2-1/2-minute contact period by the figure representing the percentage strength of the weakest lethal dilution of the x-disinfectant at the same period. The quotient = phenol coefficient at 2-1/2 minutes.

(b) Similarly obtain the phenol coefficient at 30 minutes contact period.

(c) Record the mean of the two coefficients obtained in (a) and (b) as the _mean phenol coefficient_, or simply as the ~Phenol Coefficient~.

The details of the Final Test of an actual determination are set out in the accompanying table.

TABLE 27

Organism employed, B. Coli Communis.

Culture Medium, Nutrient Agar (+10). Age, 24 hrs. Temp. of Incubation, 37 deg. C.

Quantities used { Culture } Emulsion 0.1 c.c. + 5 c.c. Germicide.
{ Emulsion }

Room Temperature during Experiments, 17 deg. C.

Germicide Strength Time of exposure Incubation 2-1/2 5 10 15 20 25 30 35 Time Temp. 1 Germicide-x 4% -- -- -- -- -- -- -- -- 7 days. 37 deg. C. 2 Germicide-x 3% 48 -- -- -- -- -- -- -- 7 days. 37 deg. C. 3 Germicide-x 2% 24 24 24 24 48 72 7 days. 37 deg. C. 4 Germicide-x 1% 24 24 24 24 72 24 72 7 days. 37 deg. C. 5 Germicide-x 0.5% 24 24 24 24 24 24 24 24 24 hours. 37 deg. C.

1 Phenol 1.10% -- -- -- -- -- -- -- -- 7 days. 37 deg. C. 2 Phenol 1.00% 24 7 days. 37 deg. C. 3 Phenol 0.75% 24 24 24 24 48 7 days. 37 deg. C. 4 Phenol 0.70% 24 24 24 24 24 72 7 days. 37 deg. C. 5 Phenol 0.65% 24 24 24 24 24 48 24 24 2 days. 37 deg. C.

((1.10/4.00) + (0.7/2.0)) 0.27 + 0.35 .62
Phenol Coefficient = ------------------------ = ----------- = --- = 0.31
2 2 2