456 



Transactions of the Canadian Institute. 



[Vol. VII. 



Spruce Sawdust. 



The reader will, of course, understand that in all experiments due. 

 allowance must be made for constitutional differences in individual fish. 

 Some men survive the effects of cold, hunger or poisonous drugs 

 longer than others. In the same way some species of fish, and some 

 individuals in each species, are naturally more hardy than others, and 

 can survive in poisoned water a longer time. Some are more delicately 

 organized and are, therefore, more easily killed. For example, black 

 bass fry lived longer than minnows in some of my experiments. Conse- 

 quently too much importance must not be attached to the exact number 

 of minutes or hours that a fish will live in any given strength of sawdust 

 solution. When we are dealing with vital phenomena, all we can con- 

 sider is the general average of a number of experiments. Keeping this 

 in view, some conclusions may fairly be drawn from the foregoing 

 results. 



1. White pine sawdust is by all odds the most poisonous substance, 



2. Next comes Ontario cedar. 



3. Then British Columbia cedar. 



4. Red pine, cedar bark and hemlock bark are moderately poisonous. 



5. Maple, oak, ash, elm, hemlock and spruce may all be grouped 

 together as only slightly poisonous. 



Experiments with Bark. 



From the frequent references to the pernicious effects of bark which 

 may be found in the literature of sawdust pollution, one would naturally 



