SOME EXPERIMENTS WITH DISINFECTANTS 



17 



organisms infect clothing, an exposure to a 40 per cent, solution of 

 formaline for 2 hours, and in case of anthrax spores, an exposure for 

 24 hours, is necessary. Silk threads impregnated with B. pestis were 

 found to be sterile after 2 minutes' exposure. Nils Englund recommended 

 spraying rooms with a 2 per cent, solution, afterwards closing the room for 

 24 hours. Walter found that a solution of i to 10,000 arrested the 

 growth of B. anthracis, V. cholerae, B. typhosus. Staphylococcus 

 pyogenes, and B. diphtheriae, and that slightly stronger solutions 

 sufficed to destroy these organisms. Faeces were rendered sterile by 

 a 10 per cent, solution in 10 minutes. 



The lack of uniformity in the various methods of testing the 

 germicidal power of antiseptics and disinfectants has long suggested 

 the necessity for the introduction of some standard method. It must, of 

 course, be conceded that the subject does not lend itself to the exact 

 treatment of chemical analysis. With a testing material consisting of 

 living germs always liable to variations of vitality and degrees of 

 resistance, absolute results are impossible, but, nevertheless, a degree of 

 accuracy may be attained sufficient to render the results of great 

 comparative value. It is evident at any rate that isolated observations 

 upon single antiseptics and disinfectants are of little value. It is only by 

 comparison of the germicidal action of the various disinfectants under 

 similar conditions that one can arrive at correct conclusions. With this 

 object in view, Ainslie Walker has proposed a means whereby a properly 

 systematized method of estimating the bactericidal value of disinfectants 

 may be established. He suggests that some well-known disinfectant 

 be selected as a standard — one known to give regular and consistent 

 results — such as pure phenol (carbolic acid). Briefly summarised, the 

 technique of his method is as follows : — To 5 c.c. of a 24 hours' blood- 

 heat culture in broth of the organism add 5 c.c. of the dilute disinfectant. 

 Shake, and take sub-cultures at definite intervals in suitable media. 

 Incubate for at least two days at 37° C. If an agar culture be preferred, 

 take up part of the growth on the point of a platinum needle, and 

 distribute it evenly in sterilized water ; the resulting emulsion may be 

 used in place of the broth culture, the rest of the procedure in both cases 

 being identical. A similar experiment is carried out simultaneously 

 with a dilute solution of phenol. From the results thus obtained, the 

 strength or efficiency of the disinfectant is expressed in multiples of the 



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