STERILIZATION 



49 



heated to 56 C. or 133 F. for ten minutes, and the 

 pneumonia coccus at 52 C. or 126 F. for ten minutes. 

 The tubercle bacillus is much more resistant and 

 requires from ten to twenty minutes' exposure at 70 

 C. or 158 F., varying directly with the density of the 

 medium in which it is. The spore-forming organisms 

 are characterized by a vastly greater resistance. This 



FIG. 20. Laboratory hot-air sterilizer. 



is due to the peculiar property of spores of resisting 

 deleterious agencies. 



Low temperatures are much less destructive than 

 high ones. The typhoid and diphtheria organisms 

 may resist 200 below zero C. or 300 F., while some 

 of the more delicate organisms quickly die at zero. 



In sterilization that method is chosen which will 



do the least damage to any object to be conserved. 



4 



