The Elements of Bacteriological Technique Part 127

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, 37C.

Quant.i.ties used { Culture } Emulsion 0.1 c.c. + 5 c.c. Germicide.

{ Emulsion }

Room Temperature during Experiments, 17C.

Germicide Strength Time of exposure Incubation 2-1/2 5 10 15 20 25 30 35 Time Temp.

1 Germicide-x 4% -- -- -- -- -- -- -- -- 7 days. 37C.

2 Germicide-x 3% 48 -- -- -- -- -- -- -- 7 days. 37C.

3 Germicide-x 2% 24 24 24 24 48 72 7 days. 37C.

4 Germicide-x 1% 24 24 24 24 72 24 72 7 days. 37C.

5 Germicide-x 0.5% 24 24 24 24 24 24 24 24 24 hours. 37C.

1 Phenol 1.10% -- -- -- -- -- -- -- -- 7 days. 37C.

2 Phenol 1.00% 24 7 days. 37C.

3 Phenol 0.75% 24 24 24 24 48 7 days. 37C.

4 Phenol 0.70% 24 24 24 24 24 72 7 days. 37C.

5 Phenol 0.65% 24 24 24 24 24 48 24 24 2 days. 37C.

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

APPENDIX.

METRIC AND IMPERIAL SYSTEMS OF WEIGHTS AND MEASURES.

The initial unit of the metric system is the Metre (_m._) or unit of length, representing one-fourth-millionth part of the circ.u.mference of the earth round the poles.

The unit of ma.s.s is the Gramme (_g._), and represents the weight of one cubic centimetre of water at its maximum density (viz. 4 C. and 760 mm.

mercury pressure).

The unit of the measure of capacity is the Litre (_l._), and represents the volume of a kilogramme of distilled water at its maximum density.

The decimal subdivisions of each of the units are designated by the Latin prefixes _milli_ = 1/1000; _centi_ = 1/100; _deci_ = 1/10; the multiples of each unit by the Greek prefixes _deka_ = 10; _hecto_ = 100; _kilo_ = 1000; _myria_ = 10,000.

For a comparison of the values of some of the more frequently employed expressions of the Metric System and the Imperial System, the following may be found convenient for reference:

~Length:~

1 millimetre (= 1 mm.) = 1/25 of an inch.

1 centimetre (= 1 cm.) = 2/5 of an inch.

1 inch (1") = 25 millimetres or 2-1/2 centimetres.

~Ma.s.s:~

1 milligramme (= 1 mg.) = 0.01543 grain (or approximately 1/64 grain).

1 gramme (= 1 g.) = 15.4323 grains.

1 "kilo" or kilogramme (= 1 kgm.) = 2 pounds, 3-1/4 ounces avoirdupois.

1 pound avoirdupois (= 1 lb.) = 453.592 grammes.

1 ounce avoirdupois (= 1 oz.) = 28.35 grammes.

1 grain = 0.0648 gramme or 64.8 milligrammes.

~Capacity:~

1 cubic centimetre (= 1 c.c.) = 16.9 minims imperial measure.

1 litre (= 1 _l._) = 35.196 fluid ounces imperial measure.

1 fluid ounce imperial measure (= 1 [Symbol: ounce]) = 28.42 cubic centimetres.

1 pint imperial measure (= 1 O.) = 568.34 cubic centimetres.

1 gallon imperial measure (= 1 C.) = 4.546 litres, or 10 pounds avoirdupois, of pure water at 62 F. and under an atmospheric pressure of 30 inches of mercury.