PLAXTS WHTCn CAI'SK DECAY 



in the dark. Into the fourth bottle {d) put a drop of 

 formahn, and place alongside of {h) . The fifth bot- 

 tle (e) we will subject to the heat of steam. This is 

 most conveniently done by placing the bottles in a 

 pan and inverting another pan 

 over it as a cover, or by means of 

 the apparatus shown in Fig. 206. 

 It consists of a pail (six to eight 

 inches in diameter) and two pans, 

 all preferably of graniteware (tin 

 may be used) . One pan serves as 

 a cover, while the other, which is 

 pierced with holes, serves as a 

 support. A little water is put into 

 the pail, and it is then set on a 

 stove or over a burner. The \aals 

 or other dishes are placed on the 

 support, the cover is fitted on and 

 the water is allowed to boil. When it has boiled for 

 half an hour we remove the vials. This process is 

 known as sterilizing (the apparatus is called a steam 

 sterilizer) . We place the sterilized vials in a warm 

 place in the dark, and renew the sterilizing each day 

 until they have been sterilized three days in succession. 

 Examine all of the vials ever}' day. In which does 

 the most rapid growth of bacteria occur, as shown 

 by the cloudiness of the liquid and the formation 

 of a surface film? 



206. Steam sterilizer, consist- 

 ing of a paU, a pan for 

 cover and a smaller pan 

 pierced with holes as a sup- 

 port (all should be of tin 

 or agateware). {Sectional 

 view.) 



