CHAPTER V 

 STERILIZATION 



Sterilization is the removal of germs from matter or destruction of germs 

 upon or in matter. It can be accomplished in the case of fluids, by nitration, 

 the addition of germicidal chemicals or by heat. Solids can be sterilized by 

 the addition of germicidal chemicals or by heat. 



Filtration can sterilize under the following conditions: 



1. When the pores of the filter are too small to permit the passage of bacteria. 



2. When the filtrate, uncontaminated, flows into a sterile container. 



3. When the construction of the filter and the connection of filter to filtrate 

 container are such as to prevent unfiltered fluid and air from mingling with the 

 filtrate. 



4. When the filtrate is sealed in its container before exposure to contamina- 

 tion with germs. 



To secure sterilization by this method requires the employment Ox a properly 

 selected, tightly adjusted and nicely manipulated filter and filtrate container. 

 Not easy for a tyro to do. 



In routine laboratory work, this method is seldom employed except in the 

 sterilization of therapeutic sera and such solutions as would be injured by heat. 

 The filters used are unglazed porcelain tubes which are first tested by passing 

 through them, fluids known to contain bacteria and then testing the filtrate for 

 sterility. 



Chemical Sterilization commonly referred to as disinfection, is accom- 

 plished by submerging utensils in a germicidal solution, or by mixing germicidal 

 solutions with fluid and solid substances. 



The efficacy of this method depends upon the following: 



1. The selection of a chemical which can kill germs. 



2. The selection of a chemical which is not changed to an inert substance, 

 without germicidal power, when brought into contact with .the matter con- 

 taminated with germs. 



3. The use of sufficient quantity of germicide to destroy all germs. 



4. Direct contact of germicidal agent with every germ. 



5. Maintenance of the contact for a sufficient length of time. 



6. The rate at which chemical sterilization progresses is in proportion to 

 the hydrogen ion concentration, and to some extent, increased by the presence 

 of sodium chloride. 



Chemical sterilization is restricted by these conditions which must be ful- 

 filled. It is further restricted by the uncertainty of results. Its employment 

 is limited because most germicidal chemicals cannot be easily removed from 

 substances with which they have been mixed, therefore, although sterilized, 



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