STEKILISATION 



they were destroyed in fifteen minutes by steam at 110- 

 120° C. Various modifications of the well-known Papin's 

 •digester have been devised for use in the bacteriological 

 laboratory, of which 

 •one of the best is that 

 shown in the accom- 

 panying figure. 



Owing to the much 

 more costly and cum- 

 brous nature of such 

 high-pressure steamers 

 their employment is 

 not to be recommended 

 for general purposes, 

 whilst in the sterilisa- 

 tion of a number of 

 ■substances, such as 

 sugars, albuminoids, 

 urea, &c., a tempera- 

 ture above 100° 0. 

 inapplicable in con- 

 sequence of the chemi- 

 cal changes brought 

 iibout. 



In the case of some 

 materials, such as milk, 

 it may be necessary 

 to effect sterihsation below 75° C, ix., below the tem- 

 perature of coagulation of albumen ; and in such 

 oases discontinuous sterilisation at 58-65° C. is em- 

 ployed for one to two hours on five to eight days ; to 

 this, however, subsequent reference will be made in 

 connection with the preparation of culture media. 



(2) Hot-air sterilisation, — The accompanying figure 

 shows the appearance of a hot-air sterilising oven as 



B 2 



Fig. 2. — High-pressuke Steam Steriliser 

 (Muencke). 



A, external jacket-wall of boiler ; b, steel clamp, with 

 screw s for brass lid k ; safety valve n, with lever 

 R, and adjustable weight g ; pressure-gauge m ; t, 

 aperture into which thermometer can be screwed ; 

 L, internal wall of copper boiler ; ff, brass remov- 

 able stand surrounded with copper gauze e. 



