DISINFECTION, STERILIZATION AND ANTISEPSIS. 239 



in other words, to the prevention of putrefaction, fermentation 

 and wound infection. Although in practice antisepsis usually 

 involves the destruction of bacteria as well the prevention of 

 their growth, it does not necessarily involve sterilization. Cold 

 prevents the growth of bacteria, and therefore acts as an anti- 

 septic, and yet it does not act as a germicide, as will be shown 

 later. Chloroform added to urine acts as an antiseptic, but 

 it does not kill the bacteria, for after the chloroform is evapo- 

 rated off the bacteria grow out in the urine. 



The destruction of bacteria and the prevention of their 

 growth is accomplished by both chemical and physical agents. 

 The chemical agents are some of them applicable in aqueous 

 solution, and some of them as gases. All agents which kill 

 bacteria are called germicides, but their action depends upon 

 the intensity and the length of time they are allowed to act. 

 If they are used in dilute solutions or if they are allowed to act 

 for a short time they may rapidly inhibit the growth or produce 

 some change in the bacteria affecting the physiological activity 

 of the organisms. Various permanent modifications have 

 been produced in certain bacteria by the action of germicides 

 applied in such a way as not to destroy the organisms outright. 

 Thus the anthrax bacillus has been deprived of its power 

 to form spores, it has also been made to assume graded viru- 

 lence so that it would kill mice but not sheep. These modi- 

 fications are produced by agencies which would destroy the 

 bacterium of anthrax if allowed to act with sufficient intensity. 



Germicides are all much more active when dissolved in water 

 than when dissolved in any other solvent, though it is true that 

 Epstein found that bichloride of mercury, carbolic acid, lysol 

 and thymol were more powerful when dissolved in 50 per cent, 

 alcohol than when dissolved in the same proportion in water, 

 though authorities differ on this point. Solutions in oils are 

 inert. The reason for this is that the bacterial cell is pene- 

 trated only by water, not by oil. The addition of alcohol to 



