14 BACTERIOLOGY. 



materials to be sterilized rest. Above this, comprising 

 the remaining three-fourths 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 per- 

 forations into which a thermometer and a manometer may 

 be inserted. The whole of the outer surface of the appa- 

 ratus 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, vvhieh 

 serves to diminish the loss of heat and deflection of the 

 flame through the action of draughts. The apparatus 

 is simple in construction, and the only point which is to 

 be observed while using it is the level of the water in 

 the reservoir. On the reservoir is a water-gauge which 

 indicates at all times the amount of water in the appa- 

 ratus. The amount of water should never be too small to 

 be indicated by the gauge, otherwise there is danger of 

 the reservoir becoming dry and the bottom of the appa- 

 ratus being destroyed by the direct action of the flame. 



A sterilizer now gaining favor for use in laboratories 

 is an apparatus originally intended for use in the kitchen. 

 It is the so-called "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 moderate care there is no fear of 



