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ceps to a sterilized Petri dish and allowed to dry. They 

 can then be placed in a test-tube and kept for future use. 



To ascertain the disinfecting action of a solution a 

 thread impregnated with the bacteria to be tested is im- 

 mersed in it fora given length of time, as for instance 2 

 minutes. It is then removed with sterilized forceps and 

 gently washed in sterilized water or alcohol. Finally it is 

 transferred to a tube of nutrient bouillon (10-15 c. c.) and 

 then set aside in the incubator for a week or more. Simi- 

 lar tests with exposures of 2, 5, 10, 3.0, and 60 minutes 

 should be made. 



The objections to this method are twofold and have 

 already been incidentally mentioned. In the first place 

 the bacteria on the thread may not be evenly exposed to 

 the action of the disinfectant and secondly the disinfec- 

 tant itself may be transferred to the nutrient medium. 

 The attempt is made to obviate the latter objection by 

 washing the threads and while this may be successful 

 in some cases, in others it fails. Thus mercuric chloride 

 is apparently held fast by the fibre and can only be re- 

 moved by the action of hydrogen sulphide (GEPPERT). 



(2). Cover glasses. This method was introduced by 

 Geppert and has been used bySpirig and others. Ordinary 

 microscopic cover-glasses are cut in two, cleaned and 

 rendered free from far, and finally sterilized. They are 

 then immersed in the bacterial suspension, or in bouillon 

 cultures, transferred to a sterilized wire gauze, under a 

 bell jar, and allowed to dry. To test a disinfectant a dry 

 cover-glasses is immersed in it for a given length of time 

 as in the case of the silk threads. It is then removed with 

 sterilized forceps and washed in about 400 c. c. of sterilized 

 water for about -|-| hour. Then placed in sterilized bouil- 

 lon and set aside in the incubator. 



The advantages of this method are (1) that a thin film 

 of evenly spread bacteria is employed, and (2) that the 

 cover-glass does not unite with the disinfectant, as is the 

 case with the silk threads. It is open to the objection, 



