96 BACTERIA IN DAILY LIFE 



on the Continent, have clearly shown, then, that 

 sand-filtration, when carefully carried out, offers 

 a most remarkable and obstinate barrier to the 

 passage of microbes, and there was every justifi- 

 cation in presuming that if disease organisms 

 should at any time be present in the raw un- 

 treated water, they would also undergo a similar 

 fate, as there was no reasonable ground for sup- 

 posing that they would behave any differently 

 from the ordinary harmless water bacteria. 



But this was a hypothesis only, and, however 

 satisfactory experiments in this direction made 

 in the laboratory might prove, there was always 

 the uncertainty attaching to a fact which had not 

 passed through the ordeal of practical experience. 



The answer to. this searching and all-important 

 question has been furnished in the most con- 

 clusive manner by the history of the cholera 

 epidemic in Hamburg and Altona respectively in 

 the year 1892. 



These two cities are both dependent upon the 

 River Elbe for their water-supply, but whereas in 

 the case of Hamburg the intake is situated above 

 the city, the supply for Altona is abstracted below 

 Hamburg after it has received the sewage of a 

 population of close upon 800,000 persons. The 

 Hamburg water was, therefore, to start with, 

 relatively pure when compared with that des- 



