138 MICRO-ORGANISMS IN WATER 



No. of Age of Filter No ; of C loilies 



Filter Bed Bed in days *">%*>' 



Old Works: 



^ 1 undergoing cleansing at 



the time 



No. 2 . . . . 17 . . . .32 

 No. 3 .... 7 .... 79 

 No. 4 .... 14 .... 56 



Unaltered Water 



Unfiltered Thames water from suction tank . 6,821 

 Do. do 7,104 



These works are particularly well adapted for such 

 an inquiry as this, since each individual filter bed has 

 a separate well into which the filtered water issuing 

 from it passes. There are four filters at the so-called 

 ' old ' works and six at the new works on the other 

 side of Portsmouth Road, and it is worthy of note that 

 the number of micro-organisms found in the water of 

 the old was distinctly greater than in that of the new 

 works. It should be mentioned, however, that the 

 sample from No. 1 filter was not a very satisfactory 

 one, as the water in the well was rather low at the time 

 and the bottom .was touched in collecting the sample, 

 and we are, therefore, of opinion that the result should 

 be discarded. The series is particularly interesting in 

 consequence of the different ages of the filters ; thus 

 No. 8 had only been at work for two days, whilst No. 6 

 had been at work for 32 days, and yet both were yielding 

 a filtrate containing an equally small number of micro- 

 organisms. The average number of micro-organisms 

 in the filtered waters was 27, or, excluding that from 

 No. 1 filter, in which the disturbance occurred during 

 the collection of the sample, only 19 per cubic centi- 

 metre. The average number of micro-organisms found 

 in the unfiltered water on the filter beds amounted to 

 1,264 per cubic centimetre. 



On the second occasion the filtered water of the old 



