TESTING OF DISINFECTANTS. 521 



6. The amount of disinfectant which is carried over to 

 each sub-culture. Thus, when the disinfectant is applied 

 to the bacterial suspension and, at the end of stated 

 intervals, transfers of 1-3 loopsful of the mixture are made 

 to sterilized nutrient media, a sufficient amount of the dis- 

 infectant may be carried over to prevent the growth of the 

 organism although it may 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 sub- 

 stance 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 in all cases the first action of a disinfectant is to at- 

 tenuate 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 chloride on anthrax spores. / Formerly, it was 

 supposed that these were killed by this substance in a 

 strength of 1-1000 in one minute. If the mercury which is 

 held fast by the silk thread, and which cannot be removed 

 by mere washing, is rendered inert by the action of 

 hydrogen sulphide it can be shown that the organism is 

 alive and infectious even after an exposure of 4 hours. It 

 may even possess vitality after an exposure of 24 hours. 

 The first action of the disinfectant is to attenuate the organ- 

 ism, the growth of which is then prevented by mere traces 

 of mercury. One part in two million according to Geppert 

 suffices to produce this result. 



When making transplantations in the subsequent 

 work on disinfectants, the platinum wire should be provided 

 with a large loop having about 2 mm. clear diameter. The 

 droplet of mercuric chloride (1-1000) adhering to this loop 

 weighs about 10 mg. Hence, when transplanted to 10 c.c. 

 of bouillon the latter will contain mercuric chloride in the 



