CHAPTER XVII. 



DETERMINATION OF THE VALUE OF ANTISEP- 

 TICS, GERMICIDES, AND DISINFECTANTS* 



THE student must bear in mind that an antiseptic is a sub- 

 stance capable of restraining the growth of bacteria ; a germi- 

 cide, one capable of killing them. All germicides are anti- 

 septic in dilute solutions, but not all antiseptics are germi- 

 cides. Disinfectants must be germicides. 



Antiseptics are chiefly employed for purposes of preserva- 

 tion, and are largely used in the industries to protect organic 

 substances from the micro-organisms of fermentation and 

 decomposition. The problem is to secure a satisfactory 

 effect with the addition of the least possible preservative in 

 order that its presence shall not chemically destroy the good 

 qualities of the substances preserved. In the case of foods 

 it becomes necessary to use preservatives free from poisonous 

 properties. 



Disinfectants and germicides are employed for the purpose 

 of destroying germs of all kinds, and the chief problem is to 

 secure efficiency of action, rather than to endeavor to save 

 on the reagent, which would be a false economy, in that the 

 very object desired might be defeated. 



The following methods of determining the antiseptic and 

 germicidal values of various agents can be elaborated accord- 

 ing to the extent and thoroughness of the investigation to 

 be made. 



I. The Antiseptic Value. Remembering that an anti- 

 septic is a substance that inhibits bacterial growth, the de- 

 termination of its value can be made by adding varying 

 quantities of the antiseptic to be investigated to culture 

 media in which bacteria are subsequently planted. It is 

 always well to use a considerable number of tubes of bouillon 

 containing varying strengths of the reagent to be investi- 

 gated. If the antiseptic be non-volatile, it may be added 

 before sterilization, which is to be preferred ; but if volatile, 

 it must be added by means of a sterile pipet, with the greatest 



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