1 8 Tattersall & Coward, Fauna of Rostheme Mere. 



and Didy, water absorbing more than 30 parts of oxygen 

 per 100,000 must be regarded as organically impure water. 

 This is borne out by the high amount of albuminoid 

 ammonia {i.e. ammonia derived from the organic matter 

 in solution in the water) present. From what is this 

 excess of organic matter derived ? We may here point 

 out that Rostherne Mere is extremely rich in plankton at 

 all times of the year, and that a certain part of the organic 

 matter in solution must be derived from the countless 

 number of organisms which die and sink to the bottom, 

 there to decompose, but we believe that the greater part 

 of the organic matter revealed by the analysis is derived 

 from the peat hole at the north end of the lake. The 

 general flow of water in the lake will allow of the peaty 

 water from the north end influencing the entire water of 

 the mere. 



Regarded from the public health point of view and 

 judged from the chemical standpoint only, the water looks 

 suspicious. But we can see no possible source from which 

 the mere can be polluted, and the absence of nitrites in 

 the water supports the idea that the lake is uncontami- 

 nated by sewage or pollution of any kind. We have not 

 had a bacteriological examination of the water of the 

 mere made, and, of course, without such an analysis it is 

 impossible to be certain that no pollution exists. We 

 merely give our opinion that there does not appear to us 

 to be any possible source from which pollution can be 

 derived. The pollution or otherwise of water may be 

 partially judged from a consideration of the amounts of 

 free and albuminoid ammonia present. In sewage-pol- 

 luted water free ammonia is generally far in excess of the 

 albuminoid ammonia, while, on the other hand, a high 

 amount of albuminoid ammonia, associated with a low 

 percentage of free ammonia, suggests vegetable con- 



