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brought out a t the bottom and up through 10cm. of the thermostat liquid to minimize loss of heat by conduction along the wire. With such a difference in temperature of only a few degrees, radiation and conduction losses were small. The experimental results were corrected for this source of error. Procedure
The experimental procedure was to heat the Pyrex electrically after it had come to a constant temperature a t the various bath temperatures. The energy input was calculated from potentials across the heater in the glass and a standard resistance, using the divisor 4.186 to change joules to the mean gram-calorie. The resistance of the heating element was 8.714 ohms a t 25" C. with a positive temperature coefficient of 0.00015. The resistance used as a standard was 2.0366 ohms. It was made from four parallel strands of No. 30 constantan wire, loosely wound on a glass tube and protected with waxed paper. Its resistance was measured by the Wheatstone bridge method, using two different Leeds and Northrup dial decade boxes and a Kohler box. I n the calculations the possible contact resistances were taken into consideration. The results were, respectively, 2.0364, 2.0368, and 2.0365 ohms. The time of heating was exactly 3 minutes, measured to 0.2 second with a stop watch. The current was generally 0.2 ampere, and was constant during the heating period. This was effected by drawing current through an &ohm coil until the storage battery delivered unchanging current. At the right time the throwing of a switch would direct the current through the heating element of the Pyrex slug.
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The thermocouples in the slug were calibrated several times at 20-degree intervals by comparison with a carefully prepared and well-calibrated two-junction copper-constantan thermccouple. This was done by suspending both in an oil bath. The maximum rise of temperature was attained about 2 minutes after the current was turned off. The temperature would then begin to drop a t the approximate rate of 0.02" C. per minute per degree difference between the bath and the glass. At 175" C. this rate was 0.03" C. The observed temperature rise was corrected on the basis of this heat leak, which varied slightly for each determination. The correction amounted on the average to about 10 per cent of the tincorrected value. Results
The results are tabulated in Table I and satisfy the relation Specific heat = 0.1839 0.0003134(t - 20" C.)
+
Heat8 of Pyrex Glass from 25O to 175" C. SPECIFIC HEAT A v . TEMP, No. OF SPECIFIC AVERAGE BY EQUAOF PYREX DETNS.5 HEAT DEVIATION TION T a b l e I-Specific
c.
26.4 5 0.1859 +0.0006 0.1859 71.0 1 0.2009 ..... 0.1998 106.4 7 0.2111 +0.0006 0.2109 127.4 3 0.2178 +0.0006 0.2175 1 0.2261 ,.... 0.2262 155.2 172.9 5 0.2316 fO.OO1O 0.2318 0 Of the twenty-four determinations only two were omitted in averaging these results.
Literature Cited (1) Eucken and Nernst, Phrsik. Z . , 10, 586 (1909)
Variation of Phenol Coefficients of Coal-Tar Disinf ectants with Different Test Organisms' Burton G . Philbrick SKINNER,
SHERMAN & ESSBLEN,
T
H E germicidal value of a disinfectant of the phenol or coal-tar type is stated commonly in terms of its phenol coefficient. This term expresses its killing power against B. fyphosus in comparison with that of a pure phenol solution of the same dilution or strength, when tested under strictly controlled conditions of technic. The Rideal-Walker ( 2 ) and Hygienic Laboratory (3) methods are the two generally recognized procedures for such determinations. I n the first method the highest dilution of the disinfectant which kills B. typhosus in 7.5 minutes but not in 5 minutes is compared with the phenol dilution which produces the same results. I n the second method the highest dilution which kills in 5, 10, and 15 minutes, respectively, is compared with the corresponding phenol dilution and the average of the three values obtained is taken as the phenol coefficient. B . typhosus was undoubtedly selected as the test organism in these methods because disinfectants are most commonly employed against that organism and because it is readily cultivated in the laboratory. With the use of these methods there has been accumulated a definite knowledge of the actual killing power of various classes of preparations against B. Received March 25, 1930. Presented in part before the Society of American Bacteriologists, December 28, 1928. 1
I N C . . BOSTON, MASS.
typhosus, and a more general and intelligent use of disinfectants has resulted. The next logical step is to determine the germicidal action of these preparations against other pathogenic organisms. This has been done in the case of the coal-tar disinfectants, and for the purposes of this study four samples representing four grades of disinfectants that had been carefully standardized by the Rideal-Walker method were selected. These grades represent coefficients of approximately 2 to 3, 6 to 6, 9 to 10, and 20, and the samples will be referred to hereafter as 2/3, 5/6, 9/10, and 20, respectively. The organisms used were as follows: The B. typhosus (Hopkins) and the Staphylococcus aureus were from strains in use in the laboratory of the Department of Agriculture. The B. diphtheriae came from the Boston Board of Health. The Streptococcus hemolyticus was of the Dick I1 strain of S. scarlatina obtained from the Antitoxin Laboratory of the Massachusetts Department of Health. The pneumococcus came from the same laboratory and was type I. Determination of Phenol Coefficients
Since the purpose of the study was to determine the comparative germicidal properties of the disinfectants, the methods of testing were adapted to give the minimum varia-
June, 1930
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tion in medium, time, etc. The Rideal-Walker procedure The positive sputum, when thick and tenacious, was mixed was accepted as the standard method for the determination with two-thirds its volume of sterile physiological saline, and of the B . typhosus phenol coefficient. With the other or- shaken for 10 minutes. When thin and watery, the sputum ganisms the general procedures described by Reddish ( 1 ) was shaken without diluting. were employed, but with the use of the Rideal-Walker time The dilutions of the disinfectants were made in the usual intervals of 2.5, 5, and 7.5 minutes, and temperature 15" to manner by the addition of sterile distilled water. Then 8 cc. 18" C. The proportion of culture to disinfectant was main- of each dilution were measured into a 15-cc. centrifuge tube tained as 0.5 to 5 cc. of diluted disinfectant and a 4-mm. loop and 2 cc. of prepared sputum added. The tubes were closed with sterile cork stoppers, shaken for 1 minute, allowed to was adopted as the standard. In testing against Staph. aureus, the Reddish broth (5 grams rest for 1 hour, and centrifuged for 5 minutes a t about 2000 Lemco, 10 grams peptone, 5 grams sodium chloride, 1000 cc. r. p. m. The supernatant fluid was removed and the tube distilled water) was used. It was also made an integral filled up with sterile saline solution, shaken, and again centripart of the test that the staphylococcus must survive 1:70 fuged. This washing was repeated three times. The final sediment, usually rather small in amount, was diluted with phenol in a 10-minute exposure period. The use of B . diphtheriae sterile saline solution, and from 0.5 to 1.0 cc. inocucalled for a different melated intraperitoneally into dium and method. The culA study has been made of a series of coal-tar disa guinea pig. Smears of ture was carried on Loeffler's infectants representing the four strengths, or B. tyblood serum (Difco) slants this sediment were made phosus phenol coefficient values, most generally offered for 3 days, the growth then and stained to demonstrate in the market. From the results reported it is possible, the presence of the bacilscraped off and made to a if the B . typhosus phenol coefficient is known, to ascerlus. A control animal was 2 nephthelometer density tain the approximate efficiency of the disinfectant always inoculated with the with sterile saline solution. against Staph. aureus, B. diphtheriae, Strep. hemountreated sputum to test The suspension then served lyticus, and Pneumococcus, in either the presence or the virulence of the organas the culture preparation absence of organic matter. This relative efficiency from which to inoculate into ism in use. After a period against these organisms can be found in terms of phenol t h e d i l u t e d disinfectant. of 6 weeks those animals coefficiency or in terms of the maximum dilution of the At the proper i n t e r v a l s still living were killed and disinfectant which will kill the given organism in 5 after inoculation one loopautopsied and the results minutes' exposure in the presence of organic matter. ful of the inoculated seed recorded as positive or negaFurther, from that portion of the study dealing with tube mixture was transtive. B. tuberculosis, it is possible, knowing the B. typhosus ferred to a Loeffler slant, On the basis of these phenol coefficient of the coal-tar disinfectant, to ascerand from this first slant to tests Table I11 gives the tain the proper dilution of disinfectant necessary to a second. These s l a n t s maximum dilution of the render tubercular sputum sterile in an exposure period were incubated a n d t h e disinfectants which will kill of one hour. B . tuberculosis in sputum growth a t the highest concentration examined under in an exposure of 1 hour. the microscope to establish its character, Here the standard organism was taken as that Table I-Phenol Coefficients as D e t e r m i n e d w i t h Various Organisms which was not killed in a 5-minute exposure to a 1:lo0 phenol DISINFECTANT SAMPLE 5/6 2 3 9/10 20 nor by a &minute exposure to a 1:120 phenol. B. lrphosus: Without organic matter 3.2 6.5 10.0 19.0 In the cases of the streptococcus and pneumococcus the With organic matter 2.9 5.8 9.0 17.0 organisms were first enriched by culturing 24 hours in glucose .Staphylococcus aureus: Without organic matter 0 . 8 1 . 4 2 . 2 5 0 broth and then for two 24-hour periods in plain broth. A With organic matter 0.7 1.3 1.8 4 9 B. diphlheriae: beef-infusion broth was found to give better growth than a Without organic matter 2.3 4.5 7.3 18.0 beef-extract broth and the former was therefore used. With With organic matter 1.6 3.5 5.3 14.0 Streptococcus hemolyticus: the streptococcus the Difco brain-heart dehydrated medium 2.2 Without organic matter 2.7 16.0 4.4 was tried out and check results were obtained. 1.7 3.5 0.3 12.0 With organic matter Pneumococcus : To determine the effect of the presence of organic matter 3.3 6.6 10.0 23.5 Without organic matter upon the germicidal action of the disinfectants, a second 9.4 17.5 With organic matter 3.0 6.1 series of tests was made with the addition of 2 per cent of i o n Killing i n 5 M i n u t e s in Presence of peptone and 1 per cent of gelatin to the diluted disinfectant T a b l e 11-Maximum D i l u tOrganic Matter in the seed tube. DISINFECTAXT Maximum Dilution with Killing Power
From the charts of the individual tests by which the coefficients in Table I were obtained, it is possible to state the maximum dilution of a given disinfectant which will kill a given organism in a given time. If the proper dilution for use may be considered as that which in the presence of organic matter will-kill the organism in 5 minutes, Table I1 gives the proper dilutions to be used against the different organisms. Study of B. tuberculosis Since the determination of the B . tuberculosis phenol coefficient of the disinfectant was not possible, determinations were made of the maximum dilutions which would kill the virulent organism in sputum in a 1-hour period of exposure, using the following technic:
ORGAKISM B. lyphosus Slaphylococcus aureus B . diphtheriae Streplococcus hemolylicus Pneumococcus
2/3 1:226 1:35 1:120 1:120 1:250
516 1:500 1:65 1:275 1:250 1:450
9/10 1:800 1:90 1:400 1:375
1:800
20 1:1400 1:250 1:llOO 1:S50 1:1500
D i l u t i o n Killing B. tuberculosis in 1 Hour MAXTMUM DISINFECTANT EFFECTIVE DILUTION 1:20 2/ 3 1:60 516 1:80 9 10 1:200 20
Table 111-Maximum
Literature Cited (1) Reddish, J. .An.Pub. Health Assocn., 17, 320 (April, 1927). (2) Rideal and Walker, "Approved Technique of the Rideal-Walker Test," H. K. Lewis & Co.,London. (3) U. S. Pub. Health Service, Pub. Health Rept., Reprint 616 (July 8, 1921).
