178 CHEMICAL INFLUENCES. 



occasionally for disinfecting purposes, though the expense or undesirable 

 qualities prevent their common application. 



The alcohols are well known for their poisonous effects, but the value 

 of ethyl alcohol as a disinfectant is usually overestimated. It takes quite 

 strong alcoholic solutions, more than 20 per cent, to kill certain yeasts and 

 the spores of some bacteria in less than a day, and a complete sterilization 

 by alcohol in a few minutes cannot always be guaranteed even with 50 to 

 60 per cent solution. It has already been mentioned that desiccated 

 organisms are very resistant to concentrated alcohol, more so than to a 

 50 per cent mixture. Methyl alcohol is weaker, the higher alcohols, es- 

 pecially amyl alcohol, are stronger disinfectants than ethyl alcohol. They 

 all give good results in the presence of water while the absolute alcohols 

 have scarcely any effect upon desiccated bacteria. None of these alco- 

 hols in whatever concentration they may be used, can be relied upon to 

 kill bacterial spores. 



Stronger germicidal effects can be obtained by the alcohols of the 

 benzene group, of which phenol or so-called carbolic acid (C 6 H 5 OH) is the 

 simplest representative. Phenol, like ethyl alcohol, is not as effective as 

 is commonly believed. It is applied in solutions from 0.5 per cent to 5 

 per cent ordinarily, but it usually takes a long time even for the 5 per cent 

 solution to kill vegetative cells as Bad. tuberculosis or B. coli; it is 

 inefficient against anthrax spores. More powerful are the higher cyclic 

 alcohols, of which the cresols are examples. They are used extensively 

 as disinfectants and antiseptics. They are, together with phenol, coal-tar 

 constituents and are sold commercially under many different names, 

 either pure or mixed with soap or other disinfectants which make 

 them emulsify readily in water. The cresols are almost insoluble in 

 water, and not as effective in solutions as they are in emulsions. The 

 disinfecting properties of tar come from the cresol contained in it. 



Hydrocarbons are used only for laboratory experiments as very weak 

 antiseptics. The aliphatic bodies, as methane, etc., which constitute a 

 large part of coal gas, have but very little effect upon bacteria; the gas is 

 used occasionally in place of hydrogen for growing anaerobic bacteria. 

 Benzol, xylol, and toluol are antiseptics, if shaken frequently with the 

 liquid to be protected, but they are not reliable as disinfectants. The 

 same is true with the common anaesthetics, ether and chloroform. The high 

 prices of these agents forbid their general use, but they are sometimes used 

 for laboratory work. 



