330 BACTERIA 



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 ' has pointed out, 

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

 solution when transferred to the medium, and thus modi- 

 fied in culture, possibly even inhibited altogether. It is 

 unnecessary for us here to discuss every mode adopted by 

 investigators in similar researches. We may just mention 

 that the most approved methods at the present time are 

 based upon two simple plans of exposure. In one we use a 

 known volume of recent broth culture of an organism grown 

 under specified conditions. 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 practicable when 

 we are dealing with volatile bodies. In such cases a stand- 

 ard 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 expos- 

 ure. It is obvious that a very large number of modifications 

 are possible of these two simple devices for testing the bac- 

 tericidal power of chemical substances. It should be re- 

 membered that here, perhaps, more than anywhere else in 

 bacteriological research, careful control experiments are 

 absolutely necessary. 



^ Bacteriology and Infective Diseases^ p. 35. 



