BY CHEMICALS 439 



Disinfection by Chemical Substances 



The effects of chemical substances as solutions, or in spray or 

 gaseous form, upon bacteria have been observed from the earliest 

 days of bacteriology. To some decomposing matter or solution a 

 disinfectant was added and sub-cultures made. If bacteria continued 

 to develop, the disinfection had not been efficient ; if, on the other 

 hand, the sub-culture remained sterile, it was assumed that disinfec- 

 tion had been complete. From such rough-and-ready methods large 

 deductions were drawn, and it is hardly too much to say that no 

 branch of bacteriology contains such a mass of unassimilated and un- 

 assimilable statements as that relating to research into disinfectants. 

 Most of the tabulated and recorded results are conspicuous in having 

 no standard as regards bacterial growth. Yet without such a 

 standard results are not comparable. 



Silk threads, impregnated with anthrax spores, were placed in 

 bottles containing carbolic acid of various strengths, and at stated 

 periods threads were removed and placed in nutrient media, and 

 development or otherwise observed. But, as Professor Crookshank 

 pointed out, this method is fallacious, the thread being still wet with 

 the solution when transferred to the medium, and thus the culture 

 was modified or even inhibited altogether.* It is unnecessary for us 

 here to discuss every mode adopted by investigators in similar 

 researches. We may, however, point out that the most approved 

 methods at the present time are based more or less upon two simple 

 modes of exposure. In one a known volume of recent broth culture 

 of an organism grown under specified conditions is used, and to this 

 is added a measured quantity of the antiseptic. At stated periods 

 loopfuls of the broth and antiseptic mixture are sub-cultured in 

 fresh-sterilised broth, and resulting development or otherwise closely 

 observed. The other method is practised in dealing with volatile 

 bodies. In such cases a standard culture is made of the organism in 

 broth at a standard temperature. Into this are dipped small strips 

 of sterilised linen. When thoroughly impregnated, these are 

 removed from the broth and subsequently dried over sulphuric acid 

 in a vacuum at 38 C. These may now be exposed for a longer or 

 shorter period to the fumes of the antiseptic in question, and broth 

 cultures made at the end of the exposure. It is obvious that a very 

 large number of modifications are possible of these two simple 

 devices for testing the bactericidal power of chemical substances. It 

 should be remembered that here, perhaps, more than anywhere else 

 in bacteriological research, careful "control" experiments are 

 absolutely necessary. 



Kecently, Ainslie Walker suggested various conditions of experi- 



* Bacteriology and Infective Diseases, p. 35. 



