STERILIZATION OF BLOOD SERUM 



125 



known as the fractional sterilization of Tyndall. Its principle is as 

 follows: When culture media are heated for a short time at a higher 

 temperature (for example for thirty minutes at 60 to 100 C.), all 

 adult vegatative forms of bacteria are destroyed. Many spores, 

 however, survive this treat- 

 ment. If, after having been FIG. 57 

 heated, the medium is left in 

 a warm place for twenty-four 

 hours, most of the remaining 

 live spores will develop into 

 vegetative forms. These are 

 killed by another short expos- 

 ure to heat. Several repeti- 

 tions of this process enable 

 all the spores to develop and 

 bring about the destruction 

 of all the bacteria. Culture 

 media containing gelatin are, 



FIG. 56 



Arnold steam sterilizer. 



Autoclave, or digester, used for sterilizing 

 under pressure. 



therefore, sterilized by placing them on three or four consecutive 

 days in the steam sterilizer for periods of from twenty to thirty min- 

 utes, and keeping them in the intervals in a warm place. 



Sterilization of Blood Serum or Transudates Containing Blood Plasma. 

 This is accomplished in the following manner: The fluid is collected 



