92 BACTERIOLOGY 



vived when heated to 55° C, then similar tests are made for 

 the same length of time for each degree of temperature 

 between 55° and 60° C. It will usually be found that heating 

 for ten minutes suffices to kill the bacteria at a temperature 

 one or two degrees lower than that required when heated 

 for only five minutes. All such tests should be made at 

 least in duplicate, and the mean of the results taken. 



CHEMICAL STERILIZATION AND DISINFECTION. 



As has been stated, it is possible by means of certain 

 chemical substances to destroy all bacteria and their spores 

 that may be within or upon various materials and objects — • 

 i. e., to sterilize them; and it is also possible by the same 

 means to rob objects of their dangerous infective properties 

 without at the same time sterilizing them — i. e., to disinfect 

 them. This latter process depends upon the fact that the 

 vitality of many of the less resistant pathogenic organisms 

 is easily destroyed by an exposure to particular chemical 

 substances that may be without effect upon the more resis- 

 tant saprophytes and their spores that are present. 



In general, the use of chemicals for sterilization is not to 

 be considered in connection with substances that are to be 

 employed as culture-media, and their employment is re- 

 stricted in the laboratory to materials that are of no further 

 value, and to infected articles that are not injured by the 

 action of the agents used, though exceptionally such vola- 

 tile germicides as chloroform and ether are employed for 

 the sterilization of special culture-media. (See Preservation 

 of Blood-serum with Chloroform.) In short, they are mainly 

 of value in rendering infected waste-material innocuous. 

 For the successful performance of this form of disinfection 



