CHAPTER VI. 



STERILIZATION AND DISINFECTION. 



Sterilization. This is the killing of all living things in 

 or upon the object or substance sterilized. The application 

 of sterilization is of the greatest importance in bacterio- 

 logical work as well as in the practical application of bac- 

 teriology in medicine, surgery and sanitary science generally. 

 In order to procure sterilized substances or media a number 

 of procedures are employed. In general it may be stated 

 that sterilization is produced by the application of heat, cer- 

 tain chemicals as disinfectants and in certain instances by 

 filtration. Where, it can be used, heat is the most effective 

 agent in securing this condition, although chemicals are 

 sometimes necessary. In order to know that an article is 

 sterilized it is necessary to apply sufficient heat to kill any 

 and all microorganisms that may be present. This may be 

 accomplished by a very high temperature for a short time 

 or a lower temperature for a longer period. Some bacteria 

 are killed by a much lower temperature or with weaker solu- 

 tions of disinfectants than others. In specific work it is 

 necessary to know the thermal death point of each species 

 of bacteria with which one is dealing and to determine the 

 strength of the commonly used disinfectants that is neces- 

 sary to kill them. In sterilizing any substance or article it 

 is necessary to bear in mind the effect of the agent used upon 

 the substance as well as the expense and possible conveni- 

 ence in applying it. 



Methods of sterilization. As already stated a number 

 of methods are not only possible but necessary in order to* 

 sterilize different articles. The more important of these 

 methods are as follows : 



1. Dry heat. Dry heat at a temperature of 135 C. 

 for one hour is destructive to all bacteria except perhaps 



