244 MORRIS M. WELLS 



I. IXTRODUCTIOX 



In a previous paper (Wells '15 a) the reactions and resistance 

 of fresh water fishes to alkalinit}', acidity and neutrality were 

 discussed upon the basis of experimental evidence which seemed 

 to indicate that the chemical reaction of the water (i.e., acid, 

 neutral or alkaline) in which the fishes live, is a matter of con- 

 siderable importance to fresh water fishes and probably to marine 

 fishes also (Shelf ord and Powers '15). In the present paper a 

 large number of expermients bearing upon the reactions and 

 resistance of fresh water fishes to salts is presented. Practically 

 no previous work has been published upon the reactions of fishes 

 to salts and the main part of the data presented here has to do 

 with this phase of the subject. Some interesting relations be- 

 tween acidity and resistance to salts are also presented. This 

 latter phase of the subject has been worked out in a prelimi- 

 nary way only; the more definite relations are left for further 

 investigation. 



The present investigation was begun at the suggestion of Prof. 

 V. E. Shelf ord and was carried on at the University' of Chicago 

 during the years 1912 and 1913. In the fall of 1914 operations 

 were transferred to the University of Illinois as the author 

 accompanied Dr. Shelford in his transfer to that place. 



II. THE WATER 



The differences in the water of the two institutions have been 

 discussed in the first paper of the series (Wells, 1. c). The 

 chief differences are the following: The water at Chicago comes 

 from Lake ^Michigan; as it flows from the tap in the laborator}', 

 it is slightly acid with carbon dioxide (2-3 cc. per liter), is super- 

 saturated with O2 (8-10 cc. per liter), contains 32 cc. per liter of 

 half-bound CO2 (bicarbonates) and a proportionate amount of 

 other salts. The water at the University of Illinois comes from 

 deep wells. As it flows from the tap it is strongly acid (18 

 cc. CO2 per liter), contains practically no O2 (0.12 cc. per liter) 

 and the half-bound CO2 equals 101 cc. per liter; other salts are 

 in proportion. Aeration brings the two waters to more nearly 



