CHAPTER VI. 



STERILIZATION AND DISINFECTION* 



BEFORE beginning the consideration of the methods em- 

 ployed for the artificial cultivation of individual micro- 

 organisms and the preparation of media for that purpose, it 

 is necessary to have a thorough knowledge of the principles 

 of sterilization and disinfection in order intelligently to ap- 

 ply the methods employed for the elimination or destruction 

 of others whose accidental presence might ruin our experi- 

 ments. 



The dust of the atmosphere, almost invariable in its micro- 

 organismal contamination, constantly settles upon our glass- 

 ware, pots, kettles, funnels, etc., and would certainly ruin 

 every culture-medium with which we experiment did we not 

 take appropriate measures for its purification and protection. 



To get rid of these undesirable " weeds " we make use of 

 our knowledge of the conditions destructive to bacterial life, 

 and subject the articles contaminated by them to the action 

 of heat beyond their known enduring power, or to the action 

 of chemic agents known to destroy them, or remove them 

 from fluids into which they have entered by passage through 

 unglazed porcelain. By all of these methods the articles 

 are made sterile. Anything is sterile when it contains no 

 germs of life. 



Sterilization is the act of making sterile by destroying or 

 removing all micro-organismal life, whether infectious or 

 non-infectious. Disinfection signifies the destruction of the 

 infectious agents, taking no account of those that are non- 

 infectious. A germicide is any substance that will kill 

 germs. It may be used for disinfection and for sterilization. 

 An antiseptic is a substance that will inhibit the growth of 

 micro-organisms. It does not necessarily kill them. 



The table on page 202 will serve to outline the methods 

 used for effecting sterilization or the complete destruction 

 or removal of living organisms: 



201 



