CHAPTER I. 

 STERILIZATION. 



Introduction. ' 



Section I. Sterilization by dry heat, p. 4. 



1. Sterilization in a naked flame, p. 4. 2. Sterilization by hot air, p. 4. 

 Section II. Sterilization by moist heat, p. 7. 



1. Sterilization in steam at 100 C., p. 7. 2. Sterilization in steam under 

 pressure, p. 9. 3. Sterilization by discontinuous heating, p. 12. 

 Section III. Sterilization by filtration, p. 14. 



1. The filtration of water, p. 15. 2. The filtration of culture media, p. 18 ; 

 (A) by compression, p. 18 ; (B) by aspiration, p. 19. 3. The filtration of small 

 quantities of liquid, p. 24. 

 Section IV. Sterilization by antiseptics, p. 26. 



FOB the study of any given micro-organism it is necessary to have a pure 

 culture of the organism, that is to say a culture from which all other organ- 

 isms have been excluded. Since micro-organisms are universally present 

 in air and water and in the ambient media generally, it is essential that all 

 vessels, culture media, instruments, etc., to be used in the preparation and 

 investigation of pure cultures should themselves be free from living organisms, 

 or in other words be sterile. Sterilization therefore means the destruction of 

 living micro-organisms in, [or their removal from,] materials and apparatus 

 used in bacteriological investigations. 



It would however be useless to sterilize vessels, instruments and culture 

 media unless steps were also taken to prevent them from again becoming 

 soiled (using the word in its bacteriological sense) before being put to their 

 proper use ; they must therefore be dealt with in such a manner that when 

 sterilized they are completely protected from contact with extraneous 

 organisms. 



To accomplish this, vessels with a narrow mouth such as flasks, bottles 

 and tubes are plugged with wool after being washed and before sterilization, 

 such articles as watch-glasses, dishes, etc., are wrapped in paper, [while metal 

 instruments, pipettes, etc., may be placed in a metal cylinder or box, or in 

 a piece of glass tubing of large diameter plugged with wool at the two 

 ends], 



1. Plugging with wool. To plug a narrow- mouthed vessel take a small piece 

 of non-absorbent cotton-wool, fold it by twisting it round and round, insert one 

 end into the mouth of the vessel and then force it gently to a depth of 2 to 3 cm. 

 leaving the other end projecting from the orifice. It is better that the plug should 

 be too large than too small. 



