18 BACTERIOLOGY FOR NURSES 



of the air has converted it into carbonate of lime it is practically 

 harmless. Bichloride of mercury is a powerful disinfectant under 

 some circumstances but when placed in contact with organic ma- 

 terial it forms an albuminate which renders it much less effective. 

 On this account it is not well suited to the disinfection of sputum 

 and feces. 



In applying a disinfectant whose strength is known it should 

 always be remembered that it must be present throughout the 

 entire mass in the proportion required. Thus if a disinfectant is 

 active in a 10 per cent solution it cannot be used in that strength 

 to disinfect an equal volume of infected material the mixture 

 would contain only 5 per cent of the bactericidal substance. An 

 equal volume of a 20 per cent solution would be required to give 

 10 per cent of the disinfectant in the resulting mixture. 



Methods for the standardization of disinfectants have been 

 devised whereby their relative value may be determined. Car- 

 bolic acid is used as the standard and the comparative strength 

 of other substances is stated in terms of their coefficiency. 



Even after the relative strength of a bactericidal substance is 

 known it should be remembered that the reaction of the solution 

 and the material to be disinfected must be considered. Thus if 

 an alkali such as lime is used to disinfect an acid substance, suffi- 

 cient lime must be added first to neutralize the acid and then the 

 additional amount required for disinfection must be added. 



A great number of more or less effective disinfectants have been 

 put upon the market, the most costly of which are by no means 

 the most reliable. Such well-known chemicals as carbolic acid, 

 bichlorid of mercury, lime, coal tar, creosotes, formalin, etc., give 

 a wide range of choice and in addition their advantages and limi- 

 tations are well established. 



DISINFECTANTS 



Carbolic Acid. A solution of 1 part to 1000 inhibits the growth 

 of bacteria, 1 part to 100 kills vegetative forms in from five to 

 thirty minutes, and 1 part to 20 kills most spores within a few hours 

 and all within a period of from one to four weeks. Carbolic acid 



