6 The Examination of Waters. 



purify the water drawn from the Thames for the supply of 

 London. Above the point at which the water is taken 

 there is a very large population ; but the circumstances are 

 not similar to ours; and compared to the Moorabool or 

 smaller streams which supply the reservoirs in question, the 

 Thames is a great river, and chemical changes caused by the 

 very filth that falls into it may tend to purify it ; and, 

 further, we can have no evidence whatever of the amount of 

 disease that it actually conveys. I may quote from an 

 essay on water supply, by J. H. Balfour Brown, lent to me 

 by Mr. Davidson. He says, in writing of purified sewage : — 

 "Common sense is revolted by water which is mixed with 

 sewage, and although common sense is often behind science, in 

 many cases, like children who stray before grown-up people, it 

 runs before. The chemist cannot point to the specific 

 infecting substance, but can tell you whether the water is 

 open to suspicion ; whether it is injurious to health can 

 only be determined by physiological tests. Dr. Frankland, 

 than whom we have no greater authority, says normal 

 sewage may be drunk with impunity ; water mixed with 

 healthy sewage is quite wholesome to drink; probably half 

 the population of the country (England) are drinking such 

 water." But what happens if the sewage is not healthy ? 

 I need not quote the well-authenticated instances in which 

 one single individual has contaminated a water supply, and 

 by this means has communicated the disease to hundreds; of 

 how in the village of Lausen the poisoned water had to filter 

 through a mountain range before it reached the victims, and 

 yet the filtering power of tlie mountain rocks through which 

 the water passed was sufficient to prevent the passage of 

 starch granules, showing that there was no fissure or channel 

 through which to convey solid particles. Nearer home 

 we have an instance that would be worth investigating. 

 The New South Wales Government made soakage dams 

 below the new town of Silverton, in a direct line with the 

 natural drainage, and during the late drought all water had 

 to be obtained from these dams or wells in the sand. 

 Typhoid was taken to the new town, and in a very short 

 time the local hospital was too small to hold the number of 

 typhoid patients. Recently we have had numerous filters 

 devised which pretend to prevent the passage of germs, but 

 at present I have not met with one or been able to make one 

 which answers the purpose. The high-pressure filters now 

 coming into common use, in which there is a cell of earthen- 



