LIST OF ILLUSTRATIONS. FIG. 1. Water bath, showing position of holes for seeding tubes and thermome ter in place.............. 2. Cross section of water bath, showing seeding tubes in place.. 3. Device for flaming inoculating loops.... 4. Block for subculture tubes..... Page. 34 34 34 34 I. METHOD OF STANDARDIZING DISINFECTANTS, WITH AND WITHOUT ORGANIC MATTER.1 By JOHN F. ANDERSON, Director Hygienic Laboratory, and THOMAS B. MCCLINTIC, Passed Assistant Surgeon, United States Public Health and Marine-Hospital Service. PART I. INTRODUCTION. In the Journal of Infectious Diseases 2 for January, 1911, we published an article on the bacteriological standardization of disinfectants. Since the publication of that article we have continued our work on disinfectants and have used the method, as described, in the examination and standardization of a large number of disinfectants that were purchased on the open market. For a method without the addition of organic matter it has given satisfaction, but there is now a more or less public demand for a method in which organic matter is used. Consequently we have decided to change the method as adopted by us, so that it may be used either with or without the addition of organic matter. The technic of performance in either case, however, is very similar, the method with organic matter being simply a modification of the method in which no organic matter is added. Consequently the method as published in the Journal of Infectious Diseases will first be given, and then the modification necessary, so that it may be used with organic matter, will be described. The principal reasons for taking up the work of standardization of disinfectants in the first place and for choosing the method proposed by us will also be given. With the methods formerly used in determining the value of a disinfectant in terms of its carbolic coefficient, the results that may be obtained even by the same worker are misleading and subject to wide variations. The Rideal-Walker method is now extensively used, but it is not without its faults. The Lancet method, while not as simple or as easily performed as the Rideal-Walker method, seems to be the best one so far proposed. 1 Manuscript submitted for publication Feb. 3, 1912. * Anderson, John F., and McClintic, Thomas B.: A method for the bacteriological standardization of disinfectants. Journ. Infec. Dis., vol. 8, No. 1, January, 1911, p. 1-26. * S. Rideal, and J. T. A. Walker. Journ. Roy. San. Inst., London, 1903, p. 424. "The standardization of disinfectants" [unsigned], Lancet, London, vol. 177, Nos. 4498, 4499, and 4500. Briefly stated, the carbolic coefficient in the Rideal-Walker method is arrived at by dividing the figure indicating the degree of dilution of the disinfectant that kills an organism in a given time by that expressing the degree of dilution of the carbolic acid that kills the same organism in the same time under exactly similar conditions. Leaving out details, the determination of the Rideal-Walker coefficient is substantially as follows: Certain standard conditions are considered essential to the proper performance of the test. Phenol solutions of known strength are used; cultures are grown in a standard medium, transplants being made every 24 hours; the loops used for all inoculations are of a standard size (about 4 mm. in diameter). Usually four dilutions of suitable strengths of the disinfectant to be used are made. Phenol controls of a suitable strength are also prepared. Five c. c. of each of these dilutions are placed in sterile test tubes, to which are added at intervals of one-half minute a 24-hour broth culture of B. typhosus in the proportion of 1 drop of culture to each cubic centimeter of disinfectant used (according to Partridge, 1 drop of culture equals about 0.1 c. c.). At the end of two and a half minutes a loopful of each of the mixtures is inoculated into a test tube containing 5 c. c. of standard broth, an interval of half a minute being thus allowed between taking the samples from the different dilutions. This is repeated at 5, 71⁄2, 10, 12, and 15 minutes. The broth tubes, after being incubated at 37° C. for 48 hours, are examined for growth. The results of the examination are then noted, and if suitable comparative strengths of the disinfectant and carbolic acid have been selected the carbolic acid coefficient is determined as above stated. The following table (Table 1) illustrates the manner of determining the carbolic acid coefficient of a disinfectant according to the RidealWalker method: Name, "A." Temperature of medication, 20° C. TABLE 1. Culture used, B. typhosus, 24-hour, extract broth, filtered. Early in our work it was realized that, on account of certain faults to be pointed out later, the Rideal-Walker method was not entirely satisfactory for determining the relative values of disinfectants in terms of pure phenol. When used under standard conditions as to temperature, organism, media, etc., approximately constant results may be obtained by different workers familiar with the technic; but a certain amount of dexterity which can only be obtained by practice is always necessary for carrying out the tests. The great objection to the method, however, and it is almost a vital one, is the latitude allowed in determining the coefficient. This point is strikingly brought out in the following tables (2, 3, and 4): Name, "A." TABLE 2. Temperature of medication, 20° C. Culture used, B. typhosus, 24-hour, extract broth, filtered. Name, "A." 1+ ++1 TABLE 3. Temperature of medication, 20° C. Culture used, B. typhosus, 24-hour, extract broth, filtered. Phenol coefficient. 90 ) 400 4.44 coefficient. Time culture exposed to action of Phenol coefficient. +++ ++ +++ +1 TABLE 4. Name, "A." Temperature of medication, 20° C. Culture used, B. typhosus, 24-hour, extract broth, filtered. Tables 2, 3, and 4 give the determination of the carbolic coefficient for the same disinfectant under exactly similar conditions, the experiments being done on the same day. In Table 2 the coefficient is 4.44; in Table 3 it is 5.5; in Table 4 it is 5.91. It will be seen, therefore, that, according to the bias of the operator, a coefficient may be obtained for the same disinfectant varying from 4.44 to 5.91, or a difference of 33.2 per cent truly a wide variation. With practice and by selecting for use certain strengths of the disinfectant and carbolic acid, the operator can regulate to a certain extent the time period at which the comparison will be made in determining the coefficient. Furthermore, if more than one strength of the carbolic-acid control is used, and the results show that more than one of the time periods will admit of comparison, the operator can arbitrarily select the one that will most advantageously suit the purpose of the experiment. Herein lie the principal objections to the Rideal-Walker method of determining the coefficient of disinfectants. Other minor objections to the method that may be noted are lack of definiteness in the proportion of culture added to the disinfectant, a "drop" being a variable quantity; the latitude allowed in temperature, 18° to 20° C., being a rather wide variation (see results of our experiments at temperatures from 15° to 30° C.); the use of seeding tubes 5 inches in length by inch in diameter, which, unless the tubes are handled, offer some difficulty in taking plants therefrom, and if the tubes are removed for this purpose erroneous results may be obtained by shaking from the sides of the tube organisms that have not been fully exposed to the action of the disinfectant. The coefficient, as determined by the Lancet Commission, is arrived at as follows: The figure representing the percentage strength of the weakest killing dilution of the phenol is divided by the figure repre |