1902-3.] Sawdust and Fish Life. 461 



moving water. As a result of sunlight, warmth and breeze, what had 

 been exceedingly disgusting water was changed in a fortnight to water 

 brownish in colour, without any odour, and perfectly transparent. A 

 heavy precipitate lay at the bottom. Minnows were able to live in it, 

 and soon made havoc with the mosquito larvae. In short the water had, 

 within the fortnight, changed to normal water, while that in the shade 

 still retained all its disagreeable and poisonous characters. The decay- 

 ing mass of sawdust and water was kept for three months, and up to the 

 very last showed no improvement. Slimy, a dark slate colour, foul 

 smelling, teeming with anaerobic bacteria and mosquito larvae, it was 

 utterly unfit to support any kind of fish life. 



Nutritive Relations. 



However, the connection between a few links in the chain of animal 

 life was apparent enough, viz., wood extracts supported bacteria, bacteria 

 supported mosquito larvae, and these again (after aeration of the water 

 such as would occur in running water) supported fish life. These obser- 

 vations dispose to some extent of the oft repeated charge against sawdust 

 that it destroys the food of young or newly hatched fish. When min- 

 nows relished mosquito larvae as food, and I frequently saw them eating 

 the larvae, it requires no great stretch of the scientific imagination to 

 understand how fish fry of different kinds, such as trout and salmon, 

 might subsist upon the larvae of mosquitoes and other aquatic insectSs, 

 these latter in turn subsisting upon bacteria, and the bacteria subsisting 

 upon the organic matter derived from the decaying vegetation of the 

 forest. 



Another thought comes up in connection with the presence of 

 organic matter in streams and rivers. The organic matter which passed 

 into a river when Canada was covered with forest must have been quite 

 different in character from that which this same stream receives to-day 

 from the vegetation of the farms along its valley. The surface drainage 

 from a forest must differ in kind from the surface drainage of a farm, 

 and the bacterial life in each must differ also. Moreover, the waters of 

 our smaller streams were, years ago, shaded by trees, and the varieties 

 of their bacterial life must thus have been quite different from the 

 bacterial life in sunlit streams of to-day. Consequently, it may fairly be 

 argued that the insect life, in and along the streams of an agricultural 

 district, differs both in kind and number from what characterized these 

 same streams 100 or 200 years ago. And if larval and adult insect life 

 has dwindled or disappeared, so must the fish life which subsisted 

 upon it. 



