60 BACTERIOLOGY. 



to the action of disinfectants ; and the process is, there- 

 fore, known as disinfection, though the same end can 

 also be reached by the application of heat to these arti- 

 cles. Strictly speaking, sterilization implies the oom- 

 plete 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 appli- 

 cation 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, there- 

 fore, be complete in the sense of sterilization. From this 

 we see it is possible to accomplish both sterilization and 

 disinfection as well by chemical as by thermal means. 



In practice the employment of these means is gov- 

 erned by circumstances. In the laboratory it is essen- 

 tial 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 impor- 

 tant that their original chemical composition should 

 remain unchanged. It is evident, therefore, that ster- 

 ilization 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 capable not only of de- 

 stroying all micro-organisms present, but whose pres- 

 ence 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 prop- 

 erties and thus render the material useless as a culture- 



