CHAPTER III. 



Principles of Sterilization by Heat — Methods Employed — Discontinued 

 Sterilization — Fractional Sterilization — Apparatus Employed — Sterili- 

 zation under Pressure — Sterilization by Hot Air — Thermal Death- 

 point of Bacteria — Chemical Disinfection and Sterilization — Mode 

 of Action of Disinfectants — Practical Disinfection. 



Of fundamental importance to successful bacteriological 

 manipulations are acquaintance with the principles under- 

 lying the methods of sterilization and disinfection, and 

 familiarity with the approved methods of applying these 

 principles in practice. 



In many laboratories it is customary to employ the term 

 sterilization for the destruction of bacteria by heat, and the 

 term disinfection for the accomplishment of the same end 

 through the use of chemical agents. Such distinction in the 

 use of the terms is obviously incorrect, as we shall endeavor 

 to explain. 



The laboratory application of the word sterilization for 

 the destruction of bacteria by high temperatures probably 

 arose from the circumstance that culture-media, and certain 

 other articles that it is desirable to render free from bacterial 

 life, are not treated by chemical agents for this purpose, 

 but are exposed to the influence of heat in various forms of 

 apparatus known as sterilizers; and the process is, therefore, 

 known as sterilization. On the other hand, cultures no 

 longer useful, bits of infected tissue, and apparatus generally 

 that it is desirable to render free from danger, are com- 

 monly subjected for a time to the action of chemical com- 

 pounds possessing germicidal properties — i. e., to the action 



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