CHAPTER XXII 



THE STANDARDIZATION OF DISINFECTANTS 

 AND ANTISEPTICS 



GEORGE F. REDDISH 



Baltimore 



DISINFECTANTS 



In 1881 Koch' produced the first satisfactory method of comparing the germicidal 

 efficiency of disinfectants. Sternberg and Klein, Castro and Wynter-Blyth, had al- 

 ready made a distinct step forward by their use of pure cultures. The test devised 

 by Koch is known as the "thread method"; spores of B. anthracis were used as the 

 test organism. The time necessary to kill spores dried on a silk thread was used to 

 indicate the germicidal value of the substances tested. Kronig and PauP modified 

 Koch's method by using small garnets instead of silk thread; this had certain definite 

 advantages in that much less of the germicide being tested was carried over into the 

 subculture medium. 



The Rideal- Walker method^ was the first really precise test for standardizing dis- 

 infectants and is the basis for all standard procedures used up to the present. In this 

 test the following factors are controlled: time, age of culture, choice of medium and 

 its acidity, temperature of medication and incubation, control of resistance of test or- 

 ganisms, specification of a distinct species of test organism, proportion of culture to 

 disinfectant, and the use of a definite standard germicide as control. Space will allow 

 but brief mention of the outstanding points in this test (192 1 revision). 



The culture medium is composed of 2 per cent Liebig's meat extract, 2 per cent Witte's 

 peptone, and i per cent sodium chloride in distilled water, adjusted to a reaction of -I-1.5. 

 Five-tenths of a cc. of a 24-hour culture of B. typhosus in this broth is added to 5 cc. of the 

 diluted disinfectant at 15° to 18° C. and transferred with a 4-mm. loop into 5 cc. of similar 

 broth at 2.5-, 5-, 7.5-, and lo-minute intervals and incubated at 37° C. for 48 hours. Only 

 one phenol control is used and this dilution must kill the test organisms in 7.5 minutes but 

 not in 5 minutes. A phenol coefficient is calculated by dividing the dilution of disinfectant 

 which kills the test organism in 7.5 minutes but not in 5 minutes by the dilution of phenol 

 which gives the same result. This figure is called the "Rideal-Walkcr coefficient."-* 



The Hygienic Laboratory method-^ differs from the Rideal -Walker test in the fol- 

 lowing respects (1921 revision): 



The culture medium contains 0.3 per cent Liebig's meat extract, i per cent Armour's 



' Koch, R.: Mitth. a. d. kais. Gsandhlsamle, i, 234. 1881. 



^ Kronig, B., and Paul, Th.: Zlschr.f. Hyg. u. Infectionskranhh., 25, r. 1897. 



3 Rideal, S., and Walker, J. T. A.: /. Roy. San. Inst., 24, 424. 1903. 



"Rideal, S., and Walker, J. T. A.: Approved Technique of the Rideal-Walker Test. London: 

 H. K. Lewis & Co., 1921. 



^ Hygienic Laboratory Bull. S2 . hY)x\\, igii; Reprint 675, Pub. Health Rep., ^6, 1559, 1921. 



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