THE STEAM STERILISER 



33 



the bacteria present and most of the spores, but some of the 

 latter remain and develop by the next day into adult organ- 

 isms; these are killed on heating the second time ; any organ- 

 isms that remain are finally destroyed by the third heating. 

 The steam steriliser is also conveniently employed in hasten- 

 ing the filtration of nutrient agar, in preference to the use of 

 the hot-water funnel. For this purpose the flask to receive 

 the filtrate, together with the funnel containing the medium 

 on the filter-paper, is wholly immersed in the steam. 



Fig. 5. — Pressure Steriliser. 



The High-pressure Steam Steriliser. — High-pressure steam 

 applied by means of an autoclave acts with greater rapidity 

 than ordinary steam. Owing to the costly nature of high- 

 pressure digesters, their employment is not to be recom- 

 mended for ordinary use, as no advantage accrues from 

 it. In certain cases, however, as in the sterilisation of 

 soil, the high-pressure digester may be conveniently used. 

 Globig (Zeitsch. f. Hijfiieiic, iii., p. 332, 1887) found that 

 certain spores were able to resist ordinary steaming for 



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