84 STERILIZATION, DISINFECTION, AND ANTISEPSIS. 



forms sulphurous acid, and is then an efficient germicide in as 

 low a percentage as 4 or 5 per cent. 



Formalin, in 2 to 5 per cent, strength, or as formaldehyde 

 gas, is a powerful germicide. 



A number of other substances have been recommended, 

 and have been used as germicides, but the above are of more 

 general and practical value. 



II. Enumeration of the common antiseptics would be too 

 lengthy to be stated in a book of this kind. 



In conclusion, one should bear in mind that chemical agents 

 must act directly on the bacteria cells themselves that is, 

 they must penetrate ; and that they are the more efficient the 

 more quickly they form chemical compounds with those cells 

 or, as usually expressed, the more penetrating power they 

 possess and anything that interferes with this chemical com- 

 bination interferes with the action of the disinfectant. 



QUESTIONS. 



What is meant by sterilization ? By disinfection ? 



At what temperature and how long does it take dry heat to sterilize? 



How long does it take live steam to sterilize ? 



How long does it take steam under pressure to sterilize? 



How are implements in the bacteriological laboratory sterilized? 



How are culture-media sterilized ? 



What is discontinuous or fractional sterilization by steam, and how is it 

 accomplished ? 



How is sterilization at a low temperature effected? When is it used? 

 What are its disadvantages ? 



What forms of apparatus are generally used to generate steam for sterili- 

 zation ? 



What are the only filters which can remove bacteria from liquid media? 



What are germicides or disinfectants? 



What are antiseptics? 



How would you test the value of a germicide ? 



What chemicals are generally used as disinfectants? 



State the value of carbolic acid as a disinfectant ; of bichloride of mercury ; 

 of the chlorinated lime ; of sodium carbonate ; of sulphur dioxide, and of 

 formaldehyde. 



