1896.] on the Past, Present and Fatiire Water Supply of London. C5 



Since May 1892, I have been making monthly determinations of 

 the number of microbes capable of developing on a gelatine plate in a 

 given volume of Thames water collected at the intakes of the metro- 

 politan water companies at Hampton ; and the number has varied 

 during this time between 631 and 5(3,630 per c.c, the highest numbers 

 having, as a rule, been found in winter, or when the temperature of 

 the water was low, and the lowest in summer, or when the temperature 

 was high. 



Now, besides temperature, there are two other conditions, to either 

 of which this difference may be attributed, viz. sunshine and rainfall ; 

 and I have endeavoured, by a series of graphic representations, to 

 disentangle these possible influences from each other, by placing the 

 results of the microbe determinations in juxtaposition with (1) the 

 temperature of the water at the time the samples were taken; (2) the 

 number of hours of sunshine on the day and up to the hour when the 

 sample was drawn, and on the two preceding days ; and (3) the flow 

 of the Thames over Teddington Weir on the same day, expressed 

 in millions of gallons per twenty-four hours. And, although the 

 graphic representations are confined to the Thames, the conditions 

 affecting bacterial life in this river are doubtless equally potent in 

 other rivers and streams. 



The samples for microbe cultivation were collected at about nine 

 inches below the surface of the water, in partially exhausted and 

 sealed glass tubes, the ends of which, when the tubes were lowered 

 to the required depths, were broken off by an ingenious contrivance 

 devised by my assistant, Mr. Burgess. On being withdrawn from the 

 river, the tubes were immediately hermetically sealed and packed 

 in ice for conveyance to my laboratory, where the cultivation was 

 always commenced within four hours of the time of collection. 



For the records of sunshine I am indebted to the kindness of 

 Mr. James S. Jordan, of Staines, and for gaugings of the TJiames at 

 Teddington Weir, to Mr. C. J. More, the Engineer to the Thames 

 Conservancy Board. 



The graphic representation of these collateral observations affords 

 definite evidence as to which of the three conditions, temperature, 

 sunshine and flow of the river, has the predominant influence upon 

 bacterial life in the water. The first diagram (Fig. 13) compares the 

 number of microbes per c.c. with the temperature of the water at 

 the time the sample was taken. The horizontal lines express the 

 numbers of microbes and the temperature, while the vertical lines 

 denote the months when the samples were taken. For obvious 

 reasons, the horizontal lines expressing the numbers of microbes 

 and temperatures, are numbered in opposite directions. 



The diagram shows that although coincidence between a higli 

 number of microbes and a low temperature are not wanting, some 

 other condition entirely masks the efiect, if any, of temperature. 



The next diagram (Fig. 14) institutes the comparison between the 

 number of microbes and the hours of sunshine to which the water 

 Vol. XV. (No. 90.) p 



