48 BAOTERIOLOGT. 



Sterilized, and can be accomplished by the proper appli- 

 cation of both thermal and chemical agents; while 

 disinfection, though it may, need not, of necessity, 

 insure the destruction of all living forms that are pres- 

 ent, but only those possessing the power of infecting ; 

 it may or may not, therefore, be incomplete 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 the work is 

 to be conducted are free from all 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 

 omild be thus sterilized, it would be necessary, in order 

 to accomplish this, to add to them substances capable 

 not only of destroying all micro-organisms present, 

 but the presence of such substances would prevent the 

 growth of bacteria that are to be subsequently culti- 

 vated in these media — that is to say, after performing 

 their sterilizing or germicidal function, they would, if 

 present, exhibit their antiseptic properties. The cir- 

 cumstances under which chemical sterilization or disin- 

 fection is practised in the laboratory are ordinarily either 

 those in which it is desirable to render materials free 

 from danger that are not affected by the chemical action 

 of the agents used, such as glass apparatus, etc., or where 

 destructive changes in the composition of the substances 

 . to be treated, as in the cases of old cultures, infected 



