CHAPTER IX. 



ANTISEPTICS AND DISINFECTANTS. 



IN the previous chapter several conditions were 

 alluded to which affected the growth of bacteria, 

 such as the nature of the nutrient soil, temperature, 

 light, and electricity. The effect of certain chemi- 

 cal substances, and of excessive heat and cold, 

 was also mentioned, but this constitutes a subject 

 of such practical importance that it must be con- 

 sidered more fully. 



Agents which retard the growth of bacteria are 

 generally spoken of as antiseptics as distinguished 

 from disinfectants, which altogether destroy their 

 vitality. 



Though chemical disinfectants, or germicides, 

 when diluted, act as efficient antiseptics, the con- 

 verse, that an antiseptic in a sufficiently concentrated 

 form will act as a disinfectant, is not the case. The 

 term " antiseptic," indeed, should be restricted to 

 those substances or agents which arrest the changes 

 bacteria produce, but which do not prevent their 

 springing into activity when removed to favourable 

 conditions. Thus excessive heat, which destroys 



