CHAPTER XXI. 



ANTISEPTICS. 



IN former chapters we have on several occasions mentioned 

 that a variety of substances and conditions are* capable of 

 exerting a detrimental influence on the life and growth of 

 micro-organisms. Amongst these are The presence of certain 

 substances in the nutrient soil, the temperature, and some 

 chemical products, such as those belonging to the aromatic 

 series, phenol, indol, skatol, &c. The presence of certain 

 substances in the nourishing material is, as we have seen, an 

 essential condition, cceteris paribus, for the growth and multi- 

 plication of micro-organisms. Thus pathogenic organisms 

 cannot thrive in an acid medium, they cannot thrive if proteids 

 or allied compounds and certain inorganic salts are absent ; 

 putrefactive and zymogenic organisms, on the other hand, or, 

 at any rate, some of them, are capable of thriving well in 

 acid media (e.g. the bacillus subtilis in acid hay-infusion, 

 the micrococcus urese in acid urine). Further, many (not all) 

 pathogenic organisms cannot thrive unless they are exposed to 

 a certain degree of warmth ; they thrive best at blood-heat, 

 while putrefactive and many zymogenic organisms thrive well 

 at ordinary temperatures, though of course their growth is 

 more rapid at higher temperatures, such as 30 38 C. Heat 

 above 50 or 60 C. arrests the growth of and even kills many 

 organisms, except the spores of bacilli, which, as we find on a 

 former page, survive even when exposed to the temperature of 

 boiling water for several minutes. The presence of carbolic 

 acid, phenol, thymol, salicylic acid, perchloride of mercury, 



