116 A MANUAL OF BACTERIOLOGY 



Salts of silver, lead, and copper have also found more or less use 

 at times as disinfectants, but their efficiency is not in proportion to 

 the cost of materials and the labor of preparation. 



Potassium permanganate is a readily soluble salt which is used 

 to some extent in surgery. Its value is impaired by the fact that 

 it is easUy reduced by organic substances with which it comes in 

 contact. 



Potassium bichromate is less easily reduced than the permanganate 

 and is sometimes used for sterilizing seeds. There are no instances, 

 however, in which mercuric bichloride would not do the same work 

 as well or better. 



Iodine in solution, especially in a solution of potassium iodide, is 

 toxic to bacteria and may have limited use as a disinfectant. 



All acids are more or less fatal to microorganisms, although there 

 are certain microorganisms that will resist some of them. The more 

 highly dissociated acids are the most toxic to bacteria. 



Phenol (carbolic acid) has wide use as a germicide and for contact 

 disinfection. It mixes readily with water in all proportions and 

 does not readily enter into combination with organic substances. It 

 is not as toxic to microorganisms as mercuric bichloride, and is more 

 irritating to the skin. It is usually employed in a concentration of 

 1 : 20 (5 per cent). 



Lysol and tricresol are cresol products widely used as contact 

 disinfectants. They possess efficiency without irritating the skin or 

 mucous membrane. Lysol, which contains about 60 per cent cresylic 

 acid, is generally used in solutions ranging from 1 to 3 per cent. 

 Tricresol has greater germicidal power than phenol, but is not as 

 toxic. It does not lose its germicidal power in the presence of albu- 

 mins, nor discolor metal instruments. It is used in solutions of 0.5 

 to 1.0 per cent. 



Thymol, salicylic acid, and benzoic acid are weak germicides. 

 They may be used in special cases, but cannot be relied upon to give 

 perfect sterilization. They are to be regarded as agents for retarding 

 bacterial activity rather than as sterilizing agents. 



Calcium hypochlorite and chlorine have found extensive use for 

 treating water and sewage. At the concentrations used it is seldom 

 that complete sterilization is accomplished, but it is possible to 

 reduce the number of organisms to a negligible quantity and to 

 annihilate bacteria of the colon-typhoid type. Ozone has in some 

 cases given complete sterility when applied to milk and waters, but 



