76 BACTERIOLOGY. 



For sterilization by live steam the apparatus in com- 

 mon use was for a long time the cylindrical boiler rec- 

 ommended by Koch. (See Fig. 8.) Its construction 

 is very simple, essentially that of the ordinary domestic 

 potato-steamer. It consists of a copper cylinder, the 

 lower fifth, approximately, of which is somewhat larger 

 in circumference than the remaining four-fifths and 

 serves 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 supports the articles to be 

 sterilized. Above this, comprising the remaining four- 

 fifths of the cylinder, is the chamber 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 

 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 

 apparatus. 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 ap- 

 paratus being destroyed by the direct action of the flame. 



A sterilizer that has come into very general use in 

 bacteriological laboratories is one originally intended 



