A. P. H. A. PHENOL COEFFICIENT 169 
required in accordance with the following table to obtain the desired 
final dilutions: 
TABLE XX 
| Initr1aL DILUTION 
In‘tial 
Dilution 
+Water (¢ c) 
1 20 | 1 40 | 1 80 | 1 . 160 | 1 : 320 | 1 2 64 
| 
Finau DinuTion 
4+4 1: 40 1: 80 1 : 160 1 : 820 1 : 640 1 : 1280 
A+5 1:45 | 1:90 1 : 180 1 : 360 1 : 720 1: 1440 
4+-6 1 : 50 1: 100 1 : 200 1 : 400 1 : 800 1 : 1600 
4-+-7 1: 55 1: 110 1 : 220 1 : 440 1 : 880 1: 1760 
4+-8 1 : 60 1 : 120 1 : 240 1 : 480 1 : 960 1 : 1920 
4+9 1 : 65 1 : 130 1 : 260 1 : 520 1: 1040 | 1: 2080 
4+10 1: 70 1 : 140 1 : 280 1 : 560 1: 1120; 1 : 2240 
Temperature. The standard temperature at which the organism is 
exposed to the action of the disinfectant is 20° C., but a variation of 
not more than 0.5° on either side of this figure is allowable. The tem- 
perature should be maintained by the use of a water bath, the design 
of which may be left to the individual operator. It is important, how- 
ever, that the bath be so arranged that the water will rise to a height 
greater than that of the dilution of disinfectant contained in these seed- 
ing tubes. The cultures and dilutions of disinfectants should be brought 
to a temperature of 20° C. before starting the test. In very warm 
weather, it will be found that there is a material increase in the tempera- 
ture of the water bath during the twenty-minute period. If, however, 
the bath is brought at the start to a temperature of 19.5° C. it will not 
generally exceed 20.5° C. during the test. For the determination of the 
temperature coefficient a temperature of 30° C. is also employed. 
All subcultures are incubated at 37° C. for forty-eight hours. The 
temperature of the incubator should be maintained between 36° and 38°. 
Technique. In the test of a new preparation the coefficient of which 
is unknown it will be necessary to make a set of range-finding tests. 
For this purpose use the series 1 : 40, 1 : 80, etc., at the head of the col- 
urns in the table of final dilutions and select for the actual test with 
phenol a series of final dilutions ranging from the highest dilution which 
killed in five minutes to the lowest dilution which failed to kill in twenty 
minutes. If some approximate idea of the coefficient is available, or if 
the preliminary test indicates a too extensive range of dilutions for the 
