128 Do Trout Purify or Pollute Water? [Sess. 



with a corresponding amount of pollution as the inevitable 

 result. Take, for example, the Alnwick Hill reservoir. The 

 spawn of the Limnsese are to be seen on the stones, despite the 

 scavengers in the shape of fish which people the pond. The 

 water naturally lowers through the day, leaving the spawn to 

 shrivel and dry up in the sunshine, thus destroying its fertility. 

 As the volume of water rises again in the evenings, it washes 

 the half-dried and lifeless spawn back into the reservoir, to 

 generate there millions of bacteria. 



Remove the scavengers in the water and Nature will pro- 

 vide others of a different character. Molluscs are greedily 

 devoured by a variety of waterfowl, including tufted duck, 

 pochard, scaup, golden-eye, &c, and it is needless to say that 

 most people would prefer fish to ducks in their water-supply. 

 Then there are the wading scavengers, which devour all the 

 various kinds of minute aquatic life. Loch Leven affords a 

 familiar illustration. Who has not observed, when passing in 

 the train, the numbers of peewits, curlews, oyster-catchers, red- 

 shanks, sandpipers, &c, wading in the shallow water at the 

 edge of the lake. I have frequently killed and dissected 

 numbers of those birds when feeding in such places, and on 

 examination of the contents of their gizzards I have been 

 forced to the conclusion that before I could drink of the 

 water of these lochs it would require a little of something to 

 " qualify " it. 



There is no doubt that the water must in some measure be 

 contaminated by the excreta of these birds, but the pollution 

 they cause is not to be compared to the purification they ac- 

 complish by eating up so many of the organisms referred to. 



While I believe that an amount of purification is traceable 

 to feathered scavengers, I am strongly of opinion that the 

 finny tribe are entitled to the credit of a great deal more. 

 That fish pollute water to a certain extent is, of course, mani- 

 fest, but my contention is that it is infinitesimal as compared 

 with what the pollution would be without them. I have 

 examined microscopically the pollution caused by birds, fish, 

 and molluscs, and the last-mentioned is very filthy indeed, 

 It has been asserted that fish frequently die in ponds, lakes, 

 reservoirs, &c, and that when decomposition takes place gross 

 pollution must ensue. This does not comport with my own 



