1 86 MEDICAL BACTERIOLOGY 



Method," and still later Anderson and McClintic introduced the "Hygienic 

 Laboratory Method." 



None of these methods is ideal; they are difficult and time-consuming and 

 yield only approximate results, yet they are of great value as approximate and 

 relative knowledge of disinfectant value is by far superior to total ignorance. 



Of the various methods, the "Hygienic Laboratory Method" is unquestion- 

 ably the best; especially in the United States it should always be the method 

 of choice. In "Hygienic Laboratory Bulletin, No. 82, of the Public Health 

 and Marine Hospital Service of the United States," April, 1912, Anderson and 

 McClintic describe their test in a clear, concise manner. Those intending to 

 make coefficient tests should obtain the above-mentioned bulletin. The follow- 

 ing description of the tests is quoted from Anderson and McClintic: 



PRINCIPAL FACTORS INVOLVED IN THE EXAMINATION OF DISINFECTANTS 



"Lack of attention to the different factors concerned in the examination of 

 disinfectants is responsible for a large percentage of the inconsistencies or dis- 

 crepancies in results obtained by the same or by different workers when working 

 with the same disinfectants. Unless strict attention is paid to the various in- 

 fluences involved it is useless to expect to find any method satisfactory. 



In order to better emphasize the effect of these influences upon the results 

 obtained, the various factors involved will be discussed under the appropriate 

 headings. 



TEST ORGANISM 



Unless different observers use the same species of organism there can be no 

 possibility of uniformity in results. The coefficient obtained with different 

 species may vary as much as 300 per cent. For this reason it is important that 

 one species be selected for use as the test organism. It would be highly desir- 

 able if the same strain of this species could be used by all workers in the 

 testing of disinfectants, as there is often a variation in the resistance of dif- 

 ferent strains of the same species. This objection does not apply as much to 

 the typhoid organism as to the colon bacillus, and to some other bacteria. 



We made a number of comparative tests with different strains of B. typhosus 

 and B. coli and found a very much greater difference in the resistance of differ- 

 ent strains of the colon bacillus than of the typhoid bacillus. 



It is most important that, before being used for a test, the organism be car- 

 ried over on broth daily for at least i week. In all cases a 24-hour culture 

 should be used, as there is decided difference in the resistance of a 24-hour and 

 a 48-hour culture, the latter being the more resistant. 



In order to avoid clumps in the culture the 24-hour broth culture should be 

 well shaken and then filtered through sterile filter-paper into a sterile test-tube. 

 After this it should be placed in the water bath in order that it may reach the 

 standard temperature before being added to the disinfectant dilutions. 



