STERILISATION 



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 C. is 

 inapplicable in con- 

 sequence of the chemi- 

 cal changes brought FIG. 2. HIGH-PRESSURE STEAM STERILISER 



about. 



In the case 



materials, such as milk, 

 it may be necessary 

 to effect sterilisation below 75 C., i.e., below the tem- 

 perature of coagulation of albumen ; and in such 

 cases 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 



(Muencke). 



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

 screw s for brass lid K ; safety valve x, with lever 

 11, and adjustable weight ft ; pressure-gauge M ; T, 

 aperture into which thermometer can be screwed ; 

 I,, internal wall of copper boiler ; FP, brass remov- 

 able stand surrounded with copper gauze E. 



B '1 



