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BIOLOGY AND TECHNIQUE 



i.e., by twenty minutes' exposure in the live steam sterilizer (Arnold, 

 Fig. 9, p. 70) on each of three consecutive days. During the intervals 

 between sterilizations, they should be kept at room temperature or in the 

 incubator, to permit the germination of spores which may be present. 

 Media containing animal serum or other albuminous solutions which 

 are to be sterilized without coagulation, may be sterilized in wate 

 baths, or in hot-air chambers (Fig. 10, p. 71), at temperatures varying 



Fig. 24. — Reichel Fiutbr. 



from 60° to 70° C, by the fractional method. In such cases five or 

 six exposures of one hour on succeeding days should be employed. 



By Filtration. — It is often desirable in bacteriological work to free 

 fluid from bacteria. This is frequently necessary for the sterilization 

 of blood-serum or exudate fluids, or for obtaining toxins free from bac- 

 teria. For these purposes a large variety of filters are in use. Those 

 most commonly employed are of the Chamberland-' or Berkefeld type, 

 which consist of hollow candles made of unglazed porcelain or dia- 

 tomaceous earth. Both these types are made in various grades of fine- 

 ness, upon which depend both the speed of filtration and the efficiency. 

 They are made in various forms and models, some of which are shown 



> Pasteur and Chamberland, Compt. rend, de I'acad. des sci., 1884. 



