STANDARDIZATION OF DISINFECTANTS 245 



standardization of disinfectants, which is a decided simplifica- 

 tion of the Anderson-McClintic (U. S. Public Health Service) 

 method, and it is hereby given in somewhat abbreviated form 

 (American Journal of Public Health, May, 191 2). 



I. The organism used is a vigorous culture of B. typhosus 

 grown for 24 hr. in standard bouillon culture medium at 38° C. 

 It is taken from the incubator at least 3^ hr. before using, to 

 allow gradual adjustment to changed conditions of temperature 

 before exposure to the germicide. The culture and germicidal 

 agent should always be at the same temperature before interac- 

 tion takes place. 



The 24 hr. bouillon culture is removed from the incubator 

 and kept at room temperature without agitation for about half 

 an hour. Then, without shaking the culture, as is usually done, 

 it is decanted into a specially constructed cotton filter, thus leav- 

 ing scum and large clumps on the filter and filtering the individual 

 bacteria in a practically isolated state. It is then filtered into 

 a sterile test-tube, which is subsequently shaken in order to ob- 

 tain a homogeneous filtrate and make it ready for use. 



The cotton filter for the filtration of bacterial cells is an or- 

 dinary test-tube drawn out at one end like a centrifugal tube, the 

 small end cut open and the edges smoothed with a flame. Into 

 the large end a small pledget of good quality ordinary cotton is 

 introduced as far as the constricted portion of the tube, pushed 

 gently with the forceps, taking care not to form any fissure in 

 the cotton or to leave any spaces between the cotton and tube. 

 The open end of the tube is then plugged with cotton and the 

 whole wrapped in cotton and parchment paper and sterilized by 

 dry heat as usual. Before using the cotton filter after steriliza- 

 tion, the cotton in the tube should be gently pushed back to the 

 proper place by means of a sterile pipette, so that it is in exactly 

 the same position as before sterilization. During sterilization the 

 cotton is pushed up by the tension caused by the heat and its own 



