GELATIN AND POTATO MEDIA. 



165 



steam, or for a sterilizer, as is often the case, when the 

 large Koch apparatus is employed. 



The autoclave. — As indicated heretofore, the spore, which 

 is the most resistant 

 form encountered, 

 may resist the action 

 of steam even for 

 several hours. 

 Steam escapes from 

 the ordinary Koch 

 sterilizer or its sev- 

 eral modifications, 

 at the ordinary at- 

 mospheric pressure, 

 and hence, the tem- 

 perature never ex- 

 ceeds 100°. If, how- 

 ever, the steam is 

 not allowed to 

 escape, but remains 

 confined in an appa- 

 ratus, the tempera- 

 ture of the steam 

 will rise with the 

 increase in pres- 

 sure. In this way, 

 steam having" a tem- 

 perature of 110°, 120° 

 or 130° can be readily obtained. The higher the tempera- 

 ture of the steam, the more rapidly will the resistant spores 

 be destroyed. Steam at 130°, under pressure, will destroy 

 instantaneously, spores which are able to withstand 3 or' 4 

 hours' exposure at 100°. The Pasteur school recognized, 

 at an early date, the value of steam under pressure as a 

 means of effecting sterilization and, for that reason, in 



Fig. 27. Autoclave of Lequeux (Wiesnegg). 



