58 



Br. Edward Franhland 



[Feb. 21, 



Company, who convey it to Green Lanes by an open conduit 25 miles 

 long called the New Eiver Cut, in wbicli it is mixed with a consider- 

 able volume of spring and deep-well water. 



All three river waters are affected by floods, and are, as raw 

 materials, of considerably different quality as regards organic purity, 

 as is seen in the diagram (Fig. 2). From these raw materials, by far 

 the largest volume of the metropolitan water supply is derived ; and 

 the chemical, or organic, purity of the water sent out to consumers 

 stands in direct relation to the organic purity of the raw material 

 used, as is seen from the diagrams (Figs. 3, 4 and 5), wLich show the 

 proportional amounts of organic elements in the raw and filtered 

 waters, and also the advantage of storage in excluding flood water. 

 Fig. 4 shows that floods in March and August were circumvented, but 



PKWimONAL MKWT V ORCAMC CLStCMTil' 

 IN RAW MMTEfL 



PROPORTIONAL AMOUNT OF ORGANIC ELEMENTS 

 IN THAMES WATER. 



Fig. 2. 



Fig. 3. 



not in November. The numbers in the margins of the diagrams 

 express the proportional amount of organic elements, that in the Kent 

 company's water during the nine years ending December 1876, being 

 taken as unity, as is depicted in the diagram (Fig. 5). 



Hitherto I have spoken of chemical purity, or comparative freedom 

 from organic matter only ; but the spread of diseases, such as cholera 

 and typhoid fever, through the agency of drinking water, has no con- 

 nection whatever with the chemical or organic purity of the water. 

 These diseases are propagated by living organisms of extreme 

 minuteness, to which the names hacilli, bacteria and microbes have 

 been given ; and here comes the important question, how, if at all, 

 does filtration secure immunity from these water-borne diseases ? 



To Dr. Koch, of Berlin, we are indebted for the answer to this 



