16 



STERILIZATION BY FILTRATION 



no the bougie is sound, attach an india-rubber syringe to the nozzle and 

 immerse all but the nozzle in a cylinder filled with water (fig. 12). By squeezing 

 the syringe air will be driven into the bougie, and if a fissure be present, even 



one so small as to be invisible 

 to the naked eye, bubbles of air 

 will stream out through it into 

 the water and will at once ren- 

 der it apparent. All defective 

 bougies must necessarily be 

 rejected. 



2. The filter must then be 

 sterilized. After testing the 

 bougie and while it is still wet, 

 plug the nozzle with dry wool 

 and sterilize in the autoclave 

 at 115-120C. for 20 minutes. 

 Fix the bougie in the metal 

 cylinder, withdraw the wool 

 plug, and the filter is ready for 

 use. 



3. Before drawing off sterile 

 water, flame the nozzle well 

 with a spirit flame. 



Cleansing and renovation of bougies. 1. When in use the external surface of a 

 filter soon gets soiled, and organisms are then likely to find their way through the 

 pores. It is necessary therefore that filters be frequently taken out and cleaned by 

 scrubbing with a stiff brush in a stream of running water, and re- sterilized. 



FIG. 12.- Method of testing a porcelain filter. 



FIG. 13. A muffle furnace. 



2. But this surface cleansing does not prevent the pores of the filter becoming 

 choked after a time, filtration being impeded in consequence ; when this occurs a 

 porcelain filter can be renovated by one or other of the following methods. 



(a) After scrubbing the filter autoclave it at 120 C., but before taking it out 



