1 66 SCIENCE PROGRESS. 



the propagation of the disease, and since the year 1854 no 

 case of Asiatic cholera in London has been traced to the 

 use of filtered river water. 



These are the results arrived at by the most general 

 investigation of the subject. They show that in every 

 epidemic, the mortality varied directly with the intensity of 

 the drainage pollution of the water drunk by the people ; 

 but if time permitted, a more detailed study of the 

 statistics in both epidemics would demonstrate, much more 

 conclusively, this connection between cholera mortality and 

 the pollution of drinking water — a connection which has quite 

 recently been terribly emphasised in the case of Hamburg. 



Such is the verdict with regard to cholera, and the 

 same is true of that other great water-borne disease typhoid 

 fever. But, unlike cholera, this disease is disseminated in 

 several other ways, and its presence or absence in any 

 locality may not, of necessity, have any connection with 

 drinking water, as is strikingly shown by the health 

 statistics of Manchester. 



There is no evidence whatever that, since the year 

 1869, when typhoid fever appeared for the first time as a 

 separate disease in the Registrar General's reports, it has 

 been conveyed by the water supply of the Metropolis. 

 An inspection of the diagram (No. 1) shows, it is true, a 

 greater proportional mortality during the period of imperfect 

 filtration than during the later period ; that is to say from 

 1883 when the process began to be performed with uniform 

 efficiency ; but the plotting of a similar curve for the deaths 

 by typhoid in Manchester shows that this disease arises from 

 other causes than polluted water, since the water supply 

 of Manchester, derived as it is from mountain sources, is 

 above all suspicion of this kind. These other causes have 

 during the last ten years been much mitigated in London 

 by various sanitary improvements ; whilst, as shown in 

 the diagram, there has been no corresponding mitigation 

 in Manchester. 



Although very soon after the year 1856 all the water 

 supplied to the Metropolis was obtained from sources much 

 less exposed to drainage pollution, it was still very carelessly 



