90 BACTERIOLOGY 



in the kitchen. It is called the "Arnold steam sterilizer." 

 It is very ingenious in its construction as well as economical 

 in its employment. 



The difference between this apparatus and that just 

 described is that it provides for the condensation of the 

 steam after its escape from the sterilizing chamber, and 

 returns the water of condensation automatically to the 

 reservoir, so that in practice the apparatus requires but 

 little attention, as with ordinary care there is no likelihood 

 of the water in the reservoir becoming exhausted, with the 

 consequent destruction of the sterilizer. Fig. 9 shows a 

 section through this apparatus. 



STERILIZATION UNDER PRESSURE. 



The advantages of the use of steam under pressure for 

 the purposes of sterilization have received such general 

 recognition that almost everywhere this method is sup- 

 planting the older one of intermittent sterilization with 

 streaming or live steam. By this plan one is able to accom- 

 plish, by a single exposure of fifteen minutes to steam under 

 a pressure of one atmosphere, the same end that would, 

 with streaming steam, require three exposures of fifteen 

 minutes on each of three successive days. 



For sterilization by steam under pressure several special 

 forms of apparatus exist. The principles involved in them 

 all are, however, the same. They provide for the generation 

 of steam in a chamber from which it cannot escape when 

 the apparatus is closed. Upon the cover of this chamber 

 is a safety-valve, which can be regulated so that any degree 

 of pressure (and coincidently of temperature) that is desir- 

 able may be maintained within the sterilizing chamber. 



