52 New York State 



however, cite later a few prominent records with reference to the 

 reaction of fishes to various sorts of polluted waters. In general it 

 may be said that, like other animals, fishes sometimes manifest no 

 response whatever to an abnormal and unwholesome environment. 

 In the majority of instances, however, they indicate the influence by 

 moving away from the source of the pollution or refusing to enter 

 upon polluted waters that lie directly in their natural path of move- 

 ment. In some cases, however, they manifest a desire to enter the 

 polluted waters and move towards the source of the pollution, 

 remaining in the danger zone until they are overcome by the effects 

 of the pollution. I have already called attention to observations of 

 Forbes and Richardson on the Illinois river. 



Powers of Resistance in Fishes 



The general features which enter into the case are summarized 

 by Wells (1918) thus: 



" The resistance of fishes to hurtful conditions varies with the 

 species, with age (or size and weight), with the individual (that is 

 with physiological state), and with the season. Practically all of 

 the fishes worked with are least resistant just after the breeding 

 season, or in the months of June, July and August (see Wells, 

 1916). In September the curve of resistance begins to run up, and 

 it continues to rise throughout the winter months, reaching its 

 maximum in March, April and May — that is, at the beginning of 

 the breeding season or just before. The relat ve resistance of 

 species does not seem to vary greatly with the season. Just how 

 much species vary in their relative resistance to different harmful 

 factors is a matter for further investigation. The work so far, 

 however, indicates that if species 1 is more resistant than species 2 

 to factor a, it is fairly safe to conclude that it will show a greater 

 resistance to factor b also." 



