CHAPTER VI. 

 STERILIZATION AND DISINFECTION. 



BEFORE considering the cultivation of bacteria 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 comprehend the 

 methods employed for the destruction of those bacteria whose 

 accidental presence might ruin our experiments. 



The dust of the atmosphere, as has already been shown, 

 is almost invariable in its micro-organismal contamination, 

 so that spores of micro-organisms constantly settle from it 

 upon our glassware, pots, kettles, funnels, etc., and would 

 certainly ruin every medium with which we experiment 

 did we not take appropriate measures for their destruction. 



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. 



Micro-organisms may be killed by heat or by the action 

 of chemicals, the process being generically termed steriliza- 

 tion. The term sterilization is, however, technically em- 

 ployed to denote the destruction of micro-organisms by heat, 

 in contradistinction to disinfection, which means the de- 

 struction of the micro-organisms by the use of chemic 

 agents. A chemic agent causing the death of micro- 

 organisms is called a germicide. Certain substances whose 

 action is detrimental to the vitality of micro-organisms 

 and prevents their growth amid otherwise suitable sur- 

 roundings are termed antiseptics. An object which is en- 

 tirely free from micro-organisms and their spores is said to 

 be sterile. 



The following list of germicides is chiefly extracted from 

 the work of Sternberg and Micquel : 



