STERILIZATION 5 



STERILIZATION 



Sterilization consists in the destruction of all forms of 

 life. It may be effected by various agents. As applied 

 to the practical requirements of the bacteriological lab- 

 oratory many of those agents such as electricity, sunlight, 

 etc., are of little value and are limited in their applications; 

 others are so well suited to particular purposes that their 

 use is almost entirely restricted to such applications. 



The Two General Methods of Sterilization are: 



A. Physical. 



1. Plasmolysis or Plasmoptysis. 



2. Desiccation. 



3. Heat (a) dry heat; (6) moist heat. 



4. Light. 



5. Filtration. 



6. Dialysis. 



7. Comminution. 



B. Chemical. 



1. Disinfectants, etc. 



A. PHYSICAL AGENTS 



I. Concentrated solutions destroy microorganisms by 

 withdrawing water from their cells (plasmolysis) , e.g., in the 

 preservation of food by concentrated salt or sugar solu- 

 tions. 



Microorganisms accustomed to a concentrated nutrient 

 substrate may suffer plasmoplysis (bursting of the cell) 

 if placed in a less concentrated medium. 



In either case, if they are subjected gradually to the 

 changing conditions, death is delayed or prevented. 



II. Desiccation is destructive to many microbes, espe- 

 cially those which do not form spores. For example, Ps. 

 radicicola is very sensitive to desiccation on the ordinary 

 cover-glass or on cotton. 



