458 Transactions of the Canadian Institute. [Vol. VII. 



As bark extracts, therefore, are not more poisonous than those from 

 pine and cedar woods, it seemed useless to conduct separate experi- 

 ments upon their effects. 



Decaying Sawdust. 



One objection frequently urged against the practice of throwing 

 sawdust into streams and rivers is that the decaying sawdust imparts 

 such" a disagreeable odour to the water that sensitive fish are driven 

 away to other waters not so polluted. It seemed to me, therefore, that 

 some progress might be made towards a definite conclusion in this 

 matter, if sawdust were allowed to stand for several weeks in an aquar- 

 ium and tested from time to time as to the changes going on in it, and 

 the influence of these upon fish. 



With this end in view about 1,000 grams of white pine sawdust 

 were placed in an aquarium three feet four inches long, fifteen inches 

 wide, and filled up to sixteen and a half inches deep with fresh water. 

 This was done June 24th. No water was allowed to enter or leave the 

 vessel. No direct sunlight fell upon it. 



The usual results followed, viz., a well defined layer of pale, yellow 

 water one and three-quarter inches deep formed in a few hours and lay 

 at the bottom. On top of this was the perfectly clear layer about fifteen 

 inches deep. 



After soaking for two days, bubbles of gas began to rise to the sur- 

 face of the water, but no attempt was made to analyze it. The bottom 

 yellowish layer had become so dense that no object could be seen across 

 it — a thickness of fifteen inches. Its upper surface was sharply marked 

 off from the overlying transparent water by a thin greyish layer. 

 Microscopic examination of this layer showed it to be swarming with 

 bacteria. 



At the end of a week, only about an inch at the bottom had retained 

 the original yellow colour; the next inch had changed to a yellowish 

 brown ; then came a greyish layer about one-sixteenth of an inch thick ; 

 above this, what had at first been fourteen inches of perfectly clear water 

 had turned to a dark grey, though still quite transparent. Black bass 

 fry placed in the aquarium at this time at first sank to the bottom, but 

 after meeting the poisonous extract once or twice could not subse- 

 quently be driven into it. On the contrary they swam along the top with 

 their nose just touching the surface of the water, and behaved as if suf- 

 fering from lack of air. They lived only about two hours. 



