40 Nkw Yotjk Rtvte 



environment in which onh certain strange types of living things 

 can exist, namely those which have the power to perpetuate their 

 existence tinder the unusual chemical conditions present. 



If we attempt to picture to ourselves similar conditions on the 

 surface of the land, we see how imperfect would be conclusions 

 formed in the same way that those regarding pollution are sometimes 

 based upon observations concerning the occasional presence or the 

 absence of fish. Jn an area devastated by forest fires one might 

 frequently see wild* animals of \arious sorts on the land surface or 

 flying in the air above it. Such movements might be in certain 

 regions very common if the area involved was not large, and even 

 where it was extensive the occurrence would be by no means 

 peculiar. But it does not suggest to our minds that the territory 

 itself is suited for the existence of these animals. In fact our eyes 

 take in at once the general conditions. We note the soil stripped of 

 vegetation, the evidences of the fire in ashes and charred fragments 

 of wood, and despite the presence of occasional individuals of the 

 higher types of animals, we never question the fact that the area has 

 been devastated and its life wiped out. 



The situation may be duplicated very closely in the water. 

 The fish are the largest, most powerful, and most active of 

 all water living organisms. The larger game fish with which 

 we are most familiar are the most active of all in their 

 movements in search of food. Consequently, it cannot be too 

 strongly contended that the presence or absence of these forms does 

 not yield positive and adequate evidence with regard to the pollution 

 of the stream or the general condition of the aquatic environment. 

 Yet concerning streams that are under examination with reference 

 to the quality of the waters, one frequently sees a statement to the 

 effect that fish were seen at a given point or were swimming through 

 a certain supposably polluted section. It is claimed, consequently, 

 that though the appearance of the stream had been changed, the 

 waste was not serious because fish were found in it and around it. 



Susceptibility of Fish 



In this connection it may be appropriate to call attention to the 

 difference in susceptibility between different species of fish. While 

 we are not in position to make an absolute statement on this point, it 

 appears from recent published experiments by Wells and Shelforc? 



