74 BACTERIOLOGY 



of disinfectants; and the process is, consequently, known as 

 disinfection, though the same end can also be reached by 

 the appHcation of heat to these articles. Strictly speaking, 

 sterilization implies the complete destruction of the vitality 

 of all micro-organisms that may be present in or upon the 

 substance to be sterilized, and can be accomplished by the 

 proper application of both thermal and chemical agents; 

 while disinfection, though it may insure the destruction of 

 all living forms that are present, need not of necessity do 

 so, but may be limited in its action to those only that possess 

 the power of infecting; it may or may not, therefore, be 

 complete in the sense of sterilization. From this we see it 

 is possible to accomplish both sterilization and disinfection 

 as well \>y chemical as by thermal means. 



In practice the employment of these means is governed 

 by circumstances. In the laboratory it is essential that 

 all culture-media with which work is to be conducted should 

 be free from living bacteria or their spores — they must be 

 sterile; and it is equally important that their original 

 chemical composition should remain unchanged. It is 

 evident, therefore, that sterilization of these substances 

 by means of chemicals is out of the question, for, while the 

 media could be thus sterilized, it would be necessary, in 

 order to accomplish this, to add to them substances cap- 

 able not only of destroying all micro-organisms present, but 

 whose presence would at the same time prevent the growth 

 of bacteria that are to be subsequently cultivated in these 

 media — that is to say, after performing their sterilizing 

 or germicidal function the chemical disinfectants would, 

 by their further presence, exhibit their antiseptic properties 

 and thus render the material useless as a culture-medium. 

 Exceptions to this are seen, however, in the case of certain 



