PREPARATION OF FILTER 



17 



of the autoclave compress and decompress several times. As far as it goes this 

 is an excellent method for unchoking a filter because there is no risk of damaging 

 its structure, but the regeneration is only partial. 



(&) Clean the filter as above, and dry it thoroughly : then heat it to redness in 

 a Bunsen flame. This involves considerable risk of fissuring the filter. 



(c) The best method is to heat the bougie to redness in an incinerator [or " muffle " 

 furnace] (fig. 13). 



Note. After regenerating a filter by either of the two last methods it must be 

 re-tested to make certain that it has suffered no damage. 



FIG. 14. Filtration by compression (Gay-Lussac pump). 



(d) Lastly, a filter may be regenerated by passing through it a 0'5 per cent, 

 solution of potassium permanganate, followed by a 5 per cent, solution of sodium 

 bisulphite (Guinochet). The method is less satisfactory than the foregoing. 



3. Whenever culture media containing micro-organisms have been passed through 

 a filter, the latter must be autoclaved immediately. 



B 



