CHAPTER III. 



Principles of sterilization by heat Methods employed Discontinued 

 sterilization Fractional sterilization Apparatus employed 

 Sterilization under pressure Sterilization by hot air Thermal 

 Death-point of bacteria Chemical disinfection and steriliza- 

 tionMode of action of disinfectants Practical disinfection. 



OF fundamental importance to successful bacterio- 

 logical manipulations are acquaintance with the prin- 

 ciples underlying the methods of sterilization and dis- 

 infection, 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. This 

 distinction in the use of the terms is not strictly correct, 

 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 commonly subjected for a time to the action of chem- 

 ical compounds possessing germicidal properties i. e., 



