CHAPTER VI 

 STERILIZATION AND DISINFECTION 



Before considering the methods employed for the artificial cul- 

 tivation of micro-organisms and for the preparation of media for 

 that purpose; it is necessary to have a thorough knowledge of the 

 principles of sterihzation and disinfection in order intelligently 

 to apply the methods to the eUmination or destruction of micro- 

 organisms whose accidental presence might ruin the experiments. 



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

 organismal contaminations, 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 passing . 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 Ufe, whether infectious or non-m- 

 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 outUne the methods used for 

 effecting sterilization or the complete destruction or removal of 

 living organisms: 



I. The SterDization and Protection of Instruments and Glassware. 

 — Sterilization may be accomplished by either moist or dry heat. 

 For the perfect sterilization of objects capable of withstandi;ig 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 6o°C., spore-bearers may withstand ioo°C. for an hour; 



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