WATER FILTRATION. XXV. 



enlargement of the water works; in another, in the preven- 

 tion of waste. All this, as I have said, may be left to the 

 water works management, if only it binds itself always to 

 provide a bacteriological! y sufficient water. In all cases, 

 however, in which bacteriological control is declined, it 

 will be absolutely necessary, in order to prevent mischief, 

 to subject the work to the most vigilant supervision with 

 regard to all the defects alluded to above. 



The opinion of Dr. Koch has been quoted so far, as it 

 contains, in my opinion, the rationale of the question of 

 filtration of water for human consumption. It clearly shews 

 that the work of the biologist and engineer must be in con- 

 junction to obtain satisfactory results in the interests of 

 public health. The lines laid down are those practically 

 followed in the water supply of cities of Great Britain and 

 the Continent, where sand filtration is necessary. 



It is interesting to note the results of bacteriological 

 examinations of water supplied to the metropolis of London. 

 The bulk of the water supplied to London is drawn from 

 the upper reaches of the Thames and river Lea, together 

 with the New River and wells belonging to the Kent Com- 

 pany. 



In report of March 1901 — after a continuance of floods in 

 the Thames and its tributaries, Sir Wm. Orookes, F.R.S., 

 and Professor Dewar, f.r.s., report viz.: — Our bacterio- 

 logical examination of 401 samples taken during the month 

 has given the results recorded in the following table ; 

 besides these samples we have examined 387 others from 

 special wells, standpipes, etc., making 788 samples in all : 



Micro Sps per cc. 



New River unfiltered (mean of 27 samples) ... 210 

 New River filtered (mean of 80 samples) ... 11 

 Thames unfiltered (mean of 27 samples) ... 7410 



Thames derived water from clear water wells of 

 eight Thames derived supplies — 



