190 Fortieth Annual Meeting 



goes considerable decomposition before it enters those parts of the 

 stream which contain fish. On the other hand we have found that one 

 important effect was to increase the amount of food for the young fishes, 

 that is, to increase the plankton product — not merely the total product, 

 because, of course, the volume of water is enormously greater, but to in- 

 crease the amount of plankton per cubic yard of the water, so far as we 

 can now see. Consequently Chicago has done us no harm by the waste 

 of that great city flowing into the stream. We have been giving close 

 attention to the matter and for the present we thank Chicago for 

 her sewage. 



Mr. Frank N. Clark, Northville, Mich : I was very much interested 

 in this paper, particularly because I have been acquainted with Pro- 

 fessor Forbes for thirty odd years and was engaged with him in experi- 

 mental whitefish work thirty years ago. I wish that Professor Forbes 

 could have talked further for several hours along the same Hne. 



I would like to ask Professor Forbes if he could tell us whether the 

 sewage from towns, sawmills, and other things of that kind is not 

 detrimental to the fishes, or how it is that in some portions of our 

 Great Lakes where it has appeared the whitefish have been driven out of 

 that territory; for instance, the Thunder Bay, Lake Huron region. 

 They were at one time caught in Thunder Bay River, but now are not 

 found nearer than nine miles out in the bay. If the sewage has not 

 been detrimental, why have the fish gone? 



Professor Forbes : I think, perhaps, I have already given an explana- 

 tion and answer to that question, when I said that our Illinois River 

 fishes are already adjusted to conditions which the fishes of a clear lake 

 would not tolerate. Whitefish could not Uve in the Illinois River; and 

 conditions which have proved harmless to catfish, buffalo and even the 

 bass of Illinois, would be intolerable to a whitefish. Furthermore, we 

 have no lumber mills on the Illinois. Whatever lumber interests were 

 there have been disposed of so that there is no waste of that kind. 



Mr. Titcomb : I want to get clearly from Mr. Forbes whether he 

 considers refuse from sawmills detrimental to fish life. 



Professor Forbes : I cannot say anything about that. I have never 

 been in situations or placed where there was any sawmill waste. I 

 have depended for my information in that regard simply on what I 

 have seen in print from people who have had opportunity to study that 

 subject. I do not know whether I have the correct general idea. 



Dr. George W. Field, Boston, Mass. : We have found in Massachu- 

 setts that sawdust is injurious; and in a recent letter from Professor 

 Hofer he says investigations in Germany have shown that the presence 

 of sawdust does not mechanically injure the fish, but there is some 

 effect on the epidermis of the gills which makes them susceptible to 

 other conditions, and it is indirectly very serious. 



If sewage reaches the fish in the condition of nitrates it may increase 

 the food contents of the water and thus be beneficial to the young fish 

 in furnishing more food ; but when it reaches the fish as crude sewage 

 it must be prejudicial. 



Another point in our investigations in Massachusetts is that this 



