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are made to sterilized nutrient media, a sufficient amount 

 of the disinfectant may be carried over to prevent the 

 growth of the organism which mny still possess vitality. 

 This has been a most serious source of error in the past. 

 The error is more marked, the greater the antiseptic 

 power of the disinfectant. It is of course less marked 

 where the substance has weak antiseptic properties 

 and where the transplantation occurs into relatively 

 large amounts of the nutrient medium (10 to 15 c. c.). 

 It must be remembered that probably in all cases the 

 first action of a disinfectant is to attenuate the organism 

 and that when the latter is in this condition a much 

 smaller amount of the disinfectant will act as an antiseptic 

 and prevent growth. This has been especially shown to 

 be the case with reference to the action of mercuric chlo- 

 ride on anthrax spores. Formerly it was disposed that 

 these were killed by this substance in a strength of 1 to 

 1000 in one minute but if the mercury which is held fast 

 by the silk thread, and which cannot be removed by mere 

 washing, is removed by the action of hydrogen sulphide it 

 can be shown that the organism is alive and infectious 

 even alter an exposure of four hours. It may even possess 

 vitality alter an exposure of 24 hours. The first action of 

 the disinfectant in this instance is to attenuate the organ- 

 ism the growth of which is then prevented by mere traces 

 of the mercury. One part in two million according to 

 Geppert suffices to produce this result. 



(7). Observation of the trial inoculation tubes over a 

 considerable length of time. The failure of tubes to grow 

 within 24 hours is not a positive indication that the organ- 

 ism has been destroyed by the disinfectant. In the at- 

 tenuated condition the organism will grow much more 

 slowly then it would if normal and in possession of full vi- 

 tality. Moreover, as stated already, traces of the disin- 

 fectant which are carried over in the experiment will still 

 further tend to retard the growth. For these reasons the 



