CHAPTER VI 

 STERILIZATION AND DISINFECTION 



BEFORE considering the methods employed for the artificial 

 cultivation of micro-organisms and for 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 apply the methods to the elimination or destruction of micro- 

 organisms whose accidental presence might ruin the experiments. 



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

 organismal contamination, constantly settles upon our glassware, 

 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 sub- 

 ject 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 re- 

 moving all micro-organismal life, whether infectious or non-in- 

 fectious. 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 following table will serve to outline the methods used for 

 effecting sterilization or the complete destruction or removal of 

 living organisms: 



I. The Sterilization and Protection of Instruments and Glassware. 

 Sterilization may be accomplished by either moist or dry heat. 

 For the perfect sterilization of objects capable of withstanding it, 

 tubes, flasks, dishes, etc., dry heat is always to be preferred, because 

 of its more certain action. If we knew just what organisms we had 

 to deal with, we might be able in many cases to save time and gas; 

 but though some non-spore-producing forms are killed at a tem- 

 perature of 6oC., spore-bearers may withstand iooC. .for an hour; 



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