58 INFECTION AND IMMUNITY 



a glass of water, just before drinking it, will be suf- 

 ficient to ensure the destruction of typhoid bacilli 

 present in the water is not well founded. Exact ex- 

 periments show that the bacillus of typhoid fever is 

 killed, in five hours' time, by a solution containing 

 one-half of one per cent, of citric acid. But the time 

 element must not be overlooked. However, the ex- 

 perimental evidence supports the view that the typhoid 

 bacillus or the cholera spirillum would not retain their 

 vitality very long in a strong lemonade, containing 

 one per cent, or more of citric acid. The addition of 

 sulphurous acid to water is still more effective, espe- 

 cially as regards the cholera germ, which is very sens- 

 itive to the action of acids. The addition of this acid 

 to drinking-water during the prevalence of cholera 

 has been recommended and practised, apparently with 

 good results. It has been shown by carefully con- 

 ducted experiments that one part in five hundred will 

 destroy the cholera spirillum in the course of a few 

 hours. 



The caustic alkalies all have considerable germicidal 

 value. Potash soap containing an excess of alkali 

 will destroy the typhoid bacillus in six-per-cent. so- 

 lution within thirty minutes ; and the scrubbing of 

 floors, articles of furniture, etc., with such a solution, 

 especially when used hot, is a most reliable method 

 of disinfection. Solutions of potash common lye 



