78 



THE PRESERVATION OF SERUMS METHODS 



panying illustration (Fig. 35) is quite serviceable, as the flask and 

 earthen candle-filter may be wrapped in a towel and sterilized in the 

 autoclave. The apparatus may carefully be attached to a suction 

 pump, and the serum pipeted off into the hollow of the candle and fil- 

 tered, the filtrate being removed, at the completion of the process, by 

 another sterile pipet. 



The cotton plug in the 



FIG. 35. A FILTER. 

 candle" is removed and the fluid poured within the 



me cotton plug in tne "candle is removed and tne nuid poured witnin tne 

 candle (hollow). The water is then turned on and the stop-cocks are opened; a 

 vacuum is produced within the flasks, which draws the fluid through the candle. 

 The filter is readily cleansed and sterilized (autoclave) and is quite efficient. 



Preservation in Fluid Form, by Freezing. Freezing a serum often 

 renders it cloudy or causes a precipitate to be deposited, and interferes 

 with the usefulness of a serum that should be absolutely clear. Freezing 

 is the only practicable method so far devised for the preservation of 

 thermolabile substances, such as complement. A small apparatus, 



