1866.] rvith the supply of water to Calcutta, 223 



possessed of any such striking properties as to aid us much, as they 

 are mostly of a neutral nature without active chemical or physical 

 characteristics. Nitrogenous bodies, however, yield products more 

 readily recognised, and as it is this class of substances which are most 

 likely to possess properties injuriously affecting the animal economy, 

 their detection is also the most important. 



The ultimate products of the decomposition of nitrogenous organic 

 substances are, in addition to water and carbonic acid, also ammonia, 

 and where excess of oxygen is present, nitric acid. But there are also 

 numerous intermediate products, and these are often characterised by 

 offensive smells which give a certain character to the putrefaction of 

 animal substances, different from that yielded by the fermentation or 

 corruption of vegetable bodies. The smell or flavour then of a water 

 is a very good test of its purity, though it indicates rather the stage 

 of decomposition in which its organic matter exists than the amount 

 of organic matter present. And in connection with this I may 

 mention the test of keeping the water and observing the changes 

 which take place in it, the production of animalcules or of aquatic 

 vegetation. Now I have kept samples of water taken from the river 

 at all seasons for many months. Those taken during the cold and 

 hot seasons settled easily and suffered very little further change ; at 

 the most a little greenish deposit at the bottom of the bottle formed, 

 which is the case, however, with ordinary distilled water. It was very 

 different, however, with the water of the rainy season. Some water 

 taken from the river on 31st August, 1865, was kept for about two 

 or three weeks, then syphoned off the deposited mud into other clean 

 stoppered bottles in which it remained, the bottles being closed for 

 about four months, when the bottles were found to have their sides 

 covered with abundant green branching vegetation : the water was 

 again syphoned off quite clear to other clean bottles and kept for about 

 six months longer, when the same appearances were observed, though 

 to a much smaller extent. There was abundant proof in this case 

 of the presence of organic matter, probably both in the form of living 

 germs and of chemical compounds dissolved in the water. The water 

 taken during the hot season may have contained as much : possibly 

 the presence of the excess of saline matter may prevent such develop- 

 ment, but I am not prepared to give an opinion on the subject. The 



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