STERILIZATION i93 



solutions of mineral acids have long been used in medicine, 

 and have probably owed a great part of their efficiency to their 

 action against bacteria. Organic acids also possess this 

 property, as in the example of the ancient employment of 

 vinegar, and there is a great probability that the almost 

 universal practice of using vinegar or lemon juice with salads, 

 shellfish, or other foods, has been a piece of natural selection 

 founded on experience of the danger of intestinal or parasitic 

 ^diseases originating from such sources. I may quote an exped- 

 ient of my own. I added B. coli to a good table vinegar 

 iS"i per cent, acetic strength), and to the same diluted to twice 

 and to ten and fifty times its volume with distilled water. In 

 the weaker two liquids the bacillus was alive after forty minutes, 

 in the half strength it was killed in fifteen minutes, and in the 

 undiluted vinegar in five minutes. 



Vegetable acids are, of course, too expensive for treating 

 effluents, but cheap mineral acids, like sulphuric, are practicable 

 and efficient in cases of serious infection. I have found^ that 

 0*072 per cent, of sulphuric acid is effective against typhoid 

 organisms in fifteen minutes ; Kitasato practically agrees, as he 

 finds o*o8 fatal. In sterilizing with acids an additional quantity 

 must be added to balance the alkalinity of the liquid : in 

 sewage this ranges usually between 0'2 and 60 parts per 

 100,000, and 4 grammes of sulphuric acid per gallon is sufficient 

 for causing the death of the typhoid bacillus in the usual 

 drainage from an isolation hospital or other infected area. 

 The free acidity is soon neutralized when such liquid becomes 

 mixed with ordinary sewage. B. enteritidis is killed by the 

 reagent, and Sp, cholercB succumbs with great rapidity. It 

 also kills intestinal worms and their ova.^ These observations 

 suggest that it should be added to the water in which vegetables 

 are washed, especially those which are to be eaten as salads ; 

 in tropical countries these are habitually fertilized with fresh 

 manure, which may be often infected. For many purposes, 

 instead of the corrosive sulphuric acid, I have succeeded in 

 using bisulphate of soda, which is portable and not dangerous,^ 

 and is added in the proportion of 15 grains per pint, equal to 

 0*17 per cent. 



I do not know that disease has been conclusively traced to 

 vegetables which have been grown in connection with sewage 



^ Parkes and Rideal, Epidemiological Society, 1901 ; Lancet, January 26, 1901. 

 2 Galli Valerio, Bull. Soc, Vaiidoisc des Sciences Naturelles, 1902, No. 143. 

 ' Parkes and Rideal, loc. cit. 



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