37 



destructive action on bacteria. The combination of 

 heat, drying, and sunlight is extremely efficacious in 

 killing bacteria. 



The study of chemicals which exert a destructive in- 

 fluence on bacteria (disinfectants) is of great practical 

 importance. Depending on the intensity of their ac- 

 tion, we usually speak of these substances as being 

 either "germicides" (germ killers) or "antiseptics" 

 (preventing germ growth). Every germicide in diluted 

 form is an antiseptic. The conditions under which the 

 disinfectant acts is of the greatest practical importance. 

 Thus, carbolic acid acts better in 5 per cent, solution 

 than in higher concentrations, and the efficiency is 

 increased by the addition of salt, but diminished by the 

 presence of alcohol. The rate of penetration into bac- 

 terial cells decreases as the concentration increases 

 above a certain limit. The temperature at which the 

 process is carried on also has a marked influence on the 

 rate of disinfection. The presence of albuminous 

 substances largely interferes with the action of certain 

 disinfectants, notably with mercury bichlorid. The 

 following are some of the more commonly used disin- 

 fectants: 



Mercuric chlorid, also called corrosive sublimate, 

 bichlorid of mercury, or, for short, "bichlorid," while 

 strongly germicidal, has the disadvantage of being 

 extremely poisonous, of forming insoluble and inert 

 compounds with albuminous substances, and of acting 

 on metals. Despite these drawbacks, however, this is 

 one of the most commonly used disinfectants at the 

 present day. It is employed largely in the form of ready 

 made tablets, containing usually sufficient "bichlorid" to 



