T902-3.J Sawdust and Fish Life. 465 



Conclusions. 



1. Strong sawdust solutions, such as occur at the bottom of an 

 aquarium, poison adult fish and fish fry, through the agency of com- 

 pounds dissolved out of the wood cells. 



2. The overlying water in such an aquarium does not at first kill 

 fish. After about a week it does kill, but solely through suffocation, the 

 dissolved oxygen having all been used up. 



3. Bacteria multiply enormously throughout all parts of such an 

 aquarium, and through oxidation change the poisonous extracts to harm- 

 less compounds. Mosquito larvae live on the bacteria. No doubt, in 

 natural pools, other aquatic insect larvae live on bacteria also. 



4. Subsequent aeration and sedimentation of sawdust water purify 

 it, so that fish can live in it without injury. 



5. Since adult fish and black bass fry both refused to be driven into 

 pine extracts in the bottom of an aquarium after they had experienced 

 its poisonous effects, we may infer that fish would desert a river much 

 polluted with sawdust, going down stream and into tributaries to escape 

 from the disagreeable influence of sawdust extracts. 



6. No stream can be pronounced off hand as poisoned by sawdust. 

 Each stream must be studied by itself and the varying conditions must 

 be thoroughly understood before a judgment can be pronounced. The 

 chief things to be considered are (i) the quantity of sawdust, and (2) 

 the volume of water into which the sawdust is discharged. Subordinate 

 conditions are the rapidity or sluggishness of the stream, the amount of 

 sunlight or shade, and the character of the water, whether from agricul- 

 tural lands or from primitive forests. 



7. Further observations and studies along sawdust polluted streams 

 and rivers of Canada are urgently needed before more definite con- 

 clusions can be reached. 



Acknowledgments. 



Acknowledgment is due to Toronto University, the Public Library, 

 Toronto, and the Canadian Institute, for the privilege of consulting their 

 libraries in order to write the historical part of this report. 



I am under special obligations to my colleague, Prof J. C. Connell, 

 M.A., M.D., for the large number of minnows which he procured for me, 

 and which were so indispensable for the laboratory experiments. 



