1 894-95.] Do Trout Purify or Pollute Water? 129 



experience, as I have found that after a dead fish lies at the 

 bottom for a few days it then rises to the surface, floating back 

 downwards, and that, buffeted by wind and waves, it ultimately 

 gets driven ashore, when its bones are picked clean by rats, 

 carrion-crows, and other land scavengers. 



By a wise provision of Nature aquatic weeds generally grow 

 luxuriantly in sheltered bays in a lake, and any pollution 

 facilitates their growth, by which means the water is purified. 

 So much is this the case, that in my small aquarium it is 

 only necessary to change the water once or twice a-year when 

 a plant is growing, whereas without the growing plant it must 

 be changed weekly. When wandering amidst the hills, who 

 has not observed among the green - coloured moss springs 

 bubbling out from the mountain-sides, and as soon as the 

 waters of a few of them trickle down and join together so as 

 to constitute a streamlet, there trout will be found, and where 

 it would be an abuse of language to mention pollution. 



Some months ago an interesting proof was led in the Court 

 of Session which bears pretty much on the subject in hand. 

 The water trustees of the town of Falkirk sought to interdict 

 the proprietor of the Denny reservoir, from whence the town 

 is supplied, from putting some trout-fry into it. On both 

 sides scientific witnesses tendered the most conflicting state- 

 ments, some of them going the length of asserting that they 

 had examined the water carefully, that there was not food in 

 it for fish, and that the trout introduced would be sure to die 

 and pollute the water. The case lasted two days, and finding 

 I was not to be examined till the second clay, I arranged with 

 the factor of the property to have some fish caught in the lake 

 that night and forwarded by first train in the morning. I 

 thereupon marched triumphantly into court with an ashetful 

 of the fattest trout I ever witnessed. On dissecting the 

 stomachs of some of the trout I found them full of Limnseae, 

 Gammari, and the larvae of various aquatic insects. The 

 judge very properly, as I think, decided in favour of the trout. 

 It may be thought that as Lord Low, in the case just cited, 

 has laid down the law on the subject, the question at the head 

 of my paper has been answered. But the scientific evidence at 

 the trial was really of such a conflicting nature that it was 

 very evident much difference of opinion on the subject existed. 



