1858.] Drinking Waters of the Metropolis. 469 



connected with the contamination of water by organic matter were 

 related. 



It appeared, also, that water containing organic matter acted 

 on lead, and thus added another source of poisoning to its own. 

 This had been pointed out by Mr. Noad and Dr. Medlock. The 

 latter chemist held that nitrous acid was formed from the organic 

 matter which, uniting with the lead, formed a quadribasic nitrite of 

 lead. This yielded up its oxide of lead to carbonic acid, forming 

 an insoluble carbonate of lead, leaving the nitrous acid free to act 

 on further quantities of lead. Dr. Medlock explained the action 

 of distilled water on lead as resulting from the water being dis- 

 tilled from water containing organic matter. Water carefully re- 

 distilled did not act on lead. But Mr. Faraday had found that 

 water obtained Ifrom melting pure ice was the purest water that 

 could be obtained, and it was shown that this water acted on lead. 

 Organic matters in standing water underwent a kind of fermenta- 

 tion, by which carbonic acid, sulphuretted hydrogen, and other 

 gases were got rid of, and nitric acid was formed. The water thus 

 underwent a process of self- purification. This occurred in Thames 

 water, and accounted for the fact that ships were often supplied 

 with water from the Thames below London Bridge. This water 

 was dangerous to drink before or during the fermenting process. 



The appreciation of small quantities of organic matters by che- 

 mical processes, was a difficult process. During the evaporation of 

 water, the organic matters were dissipated, and not all left in the 

 evaporating basin. 



The microscope was an important aid. It detected the nature 

 of organic impurities. These consisted of dead and living animal 

 and vegetable matters. The dead consisted of the tissues of animals 

 and plants. The source of these impurities could in some in- 

 stances be made manifest. Such impurities were very manifest in 

 the Thames and surface well waters ; scarcely to be detected in 

 the deep well waters. The living matters consisted of plants and 

 animals. Amongst the plants were to be found forms of DetimiditB, 

 JJiatomacecBf and Confervcc. Some forms of the latter family were 

 especially characteristic of impure waters. One form, the Calothrix 

 nivea, was found most abundant in water containing sulphuretted 

 hydrogen. The filaments of microscopic Fungi had been found in 

 impure well water. They had been detected in several waters 

 known to have been productive of disease. The lecturer had re- 

 corded two instances ( Quarterly Journal of Microscopical Science, 

 vol. iv. p. 270), and others had been published. 



Amongst the living animals, the forms of Infusoria were most 

 abundant. These were frequently indicative of the impure condi- 

 tion of water. Eggs of the higher animals were not unfrequently 

 found in the Thames water ; and some of these undoubtedly be- 

 longed to those forms of Annulosa, which find their highest deve- 

 lopment in the human body. 



