16 



MODERN DAIEY PRACTICE. 



ascertained by its being kept for some time at a tempera- 

 ture favorable to the development of the spores possibly 

 still remaining in it. 



Method of Sterilization. Several different apparatus 

 have been constructed for sterilization of nutritive media 

 through heat. The steam sterilizing apparatus introduced 

 into bacteriology by Koch and Gaffky is generally used 

 in Northern laboratories.* If this is to be used for the 

 sterilization of milk, e.g., the substratum must be exposed 

 in the apparatus to a temperature of 212 F. (100 0.) for 

 three quarters of an hour each time on three consecutive 

 days. Other substrata require of course a different treat- 

 ment in order that the sterilization may be successful. Milk 

 may also be sterilized in a very short time by being 

 heated under pressure at 248 F. (120 0.) in a Chamberland 



* The Arnold Steam-cooker, an ordinary domestic utensil in 

 America, is admirably adapted for purposes of sterilization. (Fig. 

 13). 



Water is poured into the pan (or 

 reservoir), whence it passes slowly 

 through three small apertures into the 

 shallow copper vessel (generator) be- 

 neath, becomes converted into steam, 

 and rises through the funnel in the 

 center to the sterilizing chamber above. 

 Here it accumulates under moderate 

 pressure at a temperature of 212 F. 

 The excess of steam escapes about the 

 cover, becomes imprisoned under the 

 hood, and serves to form a steam jacket 

 between the wall of the sterilizing 

 chamber and the hood. As the steam 

 FIG. 13. is forced down from above and meets 



the air it condenses and drips back into the reservoir. W, 



STERILIZING CHAMBER 



JL 



