98 BACTERIA IN DAILY LIFE 



filtration through sand before delivery, in Hamburg 

 the Elbe water was distributed in its raw con- 

 dition as drawn from the river. 



But further testimony was afforded later to 

 the truth of these results, for during the winter, 

 whilst the cases of cholera had almost completely 

 died out in Hamburg, suddenly a most un- 

 expected and unaccountable recrudescence of the 

 epidemic occurred, and this time in Altona. This 

 outbreak could not be traced to any direct in- 

 fection from Hamburg, but must have arisen in 

 Altona itself. In all about forty -seven cases 

 were recorded between December 23rd, 1892, and 

 February I2th, 1893. A searching inquiry was 

 instituted, and it was ascertained that the number 

 of bacteria found in the filtered water, usually 

 about fifty, had during these months risen to as 

 many as 1,000 and more in about twenty drops 

 of water, clearly indicating, that the filtration of 

 the water was not being efficiently carried out. 

 That this was actually the case was proved by 

 the fact that one of the sand-filters which had 

 been cleaned during the frost had become frozen 

 over, and was not able to retain the bacteria. 

 That the outbreak did not become more serious 

 Koch ascribes to the fact that this, to all intents 

 and purposes raw untreated water, was largely 

 diluted with efficiently filtered water before de- 



