152 MICRO-OKGANISMS IN WATER 



that if disease organisms are at any time present in the 

 raw untreated water they will be similarly retained, as 

 there is no reasonable ground for supposing that they 

 should behave differently in this respect from the ordi- 

 nary harmless water bacteria. That this is no mere 

 hypothesis but an actual fact has been demonstrated 

 in the most conclusive manner by the experience re- 

 cently gained in Hamburg and Altona respectively 

 during the cholera epidemic of 1892. 1 



Hamburg and Altona Water-supplies. These two 

 cities are both dependent upon the river Elbe for 

 their water-supply, but whereas in the case of Ham- 

 burg 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 destined for the use of Altona. But what was the 

 fate of these two towns as regards cholera ? Situated 

 side by side, absolutely contiguous in fact, with nothing 

 in their surroundings or in the nature of their population 

 to especially distinguish them, in the one cholera swept 

 away thousands, whilst in the other the scourge was 

 scarcely felt ; in Hamburg the deaths from cholera 

 amounted to 1,250 per 100,000, and in Altona to but 

 221 per 100,000 of the population. So clearly defined, 

 moreover, was the path pursued by the cholera, that 

 although it pushed from the Hamburg side right up 

 to the boundary line between the two cities, it there 

 stopped, this being so striking that in one street, which 

 for some distance marks the division between these 

 towns, the Hamburg side was stricken down with 



1 ' Wasserfiltration und Cholera,' Koch. Zeitsclirift fur Hygiene, vol. 

 xiv. p. 393, 1893. ' Die Cholera in Deutschland wahrend des Winters 1892 

 bis 1893,' Koch, ibid., vol. xv. p. 89, 1893. 



