DISINFECTANTS 



109 



transferred, but the latter amounts to only 0.01 cc, so 

 that ''no growth" indicates that the culture contained 

 less than 100 surviving cells per cc. It may have contained 

 50. If the average inoculum for the determination of the 

 phenol coefficient, 100 million cells, is reduced to 50 living 

 cells per cc. in 10 minutes, it requires nearly 5 minutes 

 longer to make the entire culture sterile, i.e., to reduce 

 the survivors to 0.1 per test tube of 5 cc. 



Other Methods of Standardisation. 

 Another method suggested by Bronfenbrenner, Hershey 

 and Doubly (1938) for the standardization of disinfect- 

 ants should be mentioned here. These authors, working 

 on the theory that death is due to inactivation of enzymes, 

 measured the etfect of disinfectants upon the oxygen up- 

 take of Bacterium coli, and of liver cells (see Table 21). 

 They compared the concentrations causing an equal de- 

 crease in oxygen consumption, and thus obtained a tox- 

 icity index comparable to the therapeutic index. In 1939, 

 Ely tested this method on several disinfectants, but his 

 results were not very encouraging. 



TABLE 21 



Manometric evaluation of disinfectants by the determination of 

 the decrease in oxygen uptake. (From Bronfenbrenner, Hershey and 

 Doubly, 1938.) 



PROPOSAL OF A NEW METHOD FOR TESTING DISINFECTANTS 



^ It is possible by relatively slight changes in the tech 

 nique to measure the actual efficiency of a disinfectant a 



/ 



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