DISINFECTION 323 



action, and these are termed antiseptics. The word disin- 

 fectant is used more or less indiscriminately to cover both 

 these terms, A deodorant is, of course, a substance remov- 

 ing the odour of evil-smelling putrefactive processes. Here, 

 then, we have the common designations of substances able 

 to act injuriously on bacteria and their products outside, or 

 upon the surface of, the body. But a moment's reflection 

 will bring to our minds two facts not to be forgotten. In 

 the first place, an antiseptic applied in very strong dose, or 

 for an extended period, may act as a germicide; and, vice 

 versa, a germicide in too weak solution to act as such may 

 perform only the function of an antiseptic. Moreover, the 

 action of these disinfecting substances not only varies ac- 

 cording to their own strength and mode of application, but 

 it varies also according to the specific resistance of the pro- 

 toplasm of the bacteria in question. Examples of the latter 

 are abundant, and readers who have only assimilated the 

 simple facts set forth in these pages are aware that between 

 the bacillus of diphtheria and the spores of anthrax there 

 is an enormous difference in power of resistance. In the 

 second place, reflection will enable us to recall what has 

 already been said, when discussing the requirements neces- 

 sary for bacterial growth, respecting the physical conditions 

 injurious to development. In a cold temperature, as a gen- 

 eral rule, bacteria do not multiply with the same rapidity as 

 at blood-heat. Within the limits of a moist perimeter the air 

 is, to all intents and purposes, germ-free. Direct sunlight 

 has a definitely germicidal effect in the course of time upon 

 some of the most virulent bacteria we know. Here, then, 

 are three examples of physical agents — low temperature, 

 moist perimeter, sunlight — which, if strong enough in de- 

 gree, or acting for a long enough period of time, become 

 first antiseptics and then germicides. Yet for a limited 

 period they have no injurious effect upon bacteria. These 

 are simple points, and call for little comment, yet the pages 



