58 BACTERIOLOGY. 



Clearly, if the desired pressure and temperature have 

 been maintained for ten minutes, one cannot say that 

 this is all the heat to which the articles have been sub- 

 jected during their stay in the chamber. In this light, 

 while steam under pressure may answer very well for 

 routine sterilization, still it presents insurmountable 

 obstacles to its use in finer experiments where time ex- 

 posure to definite temperature is of importance. 



For most of the media which are employed the discon- 

 tinued method at the temperature of streaming steam 

 gives the most satisfactory results. 



For sterilization by live steam the apparatus com- 

 monly employed has, until recently, been the cylindrical 

 boiler recommended by Koch. (See Fig. 8.) 



Its construction is very simple. It consists of a 

 copper cylinder, the lower fifth of which is somewhat 

 larger in diameter than the remaining four-fifths, and 

 acts as a reservoir for the water from which the steam 

 is to be generated. Covering this section of the cylinder 

 is a wire rack or grating through which the steam 

 passes, and which serves as a bottom upon which the 

 objects to be sterilized rest. Above this, comprising 

 the remaining four-fifths of the cylinder, is the cham- 

 ber for the reception of the materials over and through 

 which the steam is to pass. The cylinder is closed by 

 a snugly-fitting cover through which are usually two 

 perforations into which a thermometer and a manometer 

 may be inserted. The whole of the outer surface of 

 the apparatus is encased in a non-conducting mantle of 

 asbestos or felt. 



The water is heated by a gas-flame placed in an en- 

 closed chamber, upon which the apparatus rests, which 

 serves to diminish the loss of heat and deflection of the 



