CHAPTER XIII. 



DISINFECTION— STERILIZATION- 

 DISINFECTANTS. 



The discussion of the physiology of bacteria in the pre- 

 ceding chapters has shown that a number of environmental 

 factors must be properly correlated in order that a given 

 organism may thrive. Conversely, it can be stated that any 

 one of these environmental factors may be so varied that 

 the organism will be more or less injured, may even be 

 destroyed by such variation. It has been the thorough study 

 of the above-mentioned relationships which has led to prac- 

 tical methods for destroying bacteria, for removing them or 

 preventing their growth when such procedures become 

 necessary. 



The process of killing all the living organisms or of remov- 

 ing them completely is spoken of as rlisinfection or as sterili- 

 zation, according to circumstances. Thus the latter term is 

 applied largely in the laboratory, while the former more 

 generally in practice outside the laboratory. So also disin- 

 fection is most commonly done with chemical agents and 

 sterilization by physical means, though exceptions are 

 numerous. The original idea of disinfection was the destruc- 

 tion of " infective" organisms, that is, organisms producing 

 disease in man or animals. A wider knowledge of bacteri- 

 ology has led to the application of the term to the destruc- 

 tion of other organisms as well. Thus the cheese-maker 

 "disinfects" his curing rooms to prevent abnormal ripening 

 of cheese, and the dairy-worker "disinfects" his premises to 

 avoid bad flavors, abnormal changes in the butter or milk. 

 Sterilization is more commonly applied to relatively small 

 objects and dinnfection to larger ones. Thus in the labor- 

 atory, instruments, glassware, apparatus, etc., are "steril- 

 ized" while desks, walls and floors are "disinfected." The 



