76 STERILIZATION, DISINFECTION, AND ANTISEPSIS. 



CHAPTER V. 



STERILIZATION, DISINFECTION, AND ANTISEPSIS! 



Definitions. The freeing of substances from the live bacteria 

 they may contain or that may have collected on their surfaces 

 is called sterilization. This is accomplished either by means 

 of heat or the use of chemicals. 



Erroneously sometimes the term sterilization is used to 

 indicate the destruction of bacteria by the application of heat, 

 the term disinfection being used then for their destruction by 

 chemical agents. 



To disinfect a substance is to destroy in it or on it all the 

 harmful or infectious bacteria, without necessarily killing all 

 the living bacteria. 



THE METHODS OF STERILIZATION. 



I. Substances chemically sterilized are unfit for bacterial 

 culture, except in very rare instances when the chemical 

 agents are very volatile. 



II. In laboratory work, therefore, where the aim is the 

 cultivation of bacteria, heat is the only method of sterilization 

 used. This is applied either in the form of dry heat or moist 

 heat (steam). 



1. All substances which may be passed through the Bunsen 

 flame and heated red-hot are usually sterilized in this manner. 



2. Other implements, such as instruments and glassware, 

 which would be injured by the direct flame, but withstand con- 

 siderable heat, are sterilized by dry heat in an oven at a 

 temperature of 160 to 180 C. for an hour. 



3. For culture-media, one resorts to sterilization by steam, 

 except in rare instances, when filtration under pressure through 

 unglazed porcelain is considered sufficient. 



Experience has taught that steam at a temperature of 

 100 C. will kill all known bacteria and their spores within 

 an hour, and Pasteur has demonstrated that steam under a 

 pressure of two or three atmospheres, at about 130 C., will 



