254 MORRIS M. WELLS. 



One thing is clear; the chemical reaction of the water should 

 be known with accuracy, in all experiments with salts and gases 

 in solution. A recognition of this fact will help to clear up some 

 of the many contradictory results which have been obtained by 

 various workers. It seems to be demonstrated beyond a doubt 

 that the toxicity of distilled water is in part due to the absence 

 or scarcity of inorganic salts, but it is also evident that the 

 neutrality of such water may be an important factor in its 

 toxicity. 



VI. GENERAL CONCLUSIONS. 



1. The chemical reaction of the water is an important factor 

 in the reactions and resistance of organisms. 



2. Fresh-water fishes select slight acidity in a gradient, when 

 the other choices are neutrality and alkalinity. They choose 

 slight alkalinity in preference to neutrality. 



3. The CO 2 optimum for the different species of fishes ex- 

 perimented upon, varies from very close to neutrality for the 

 blue-gill, to 6 c.c. per liter for the sunfishes and crappies. This 

 is for the November to January condition. At other seasons 

 and in other waters, the optimum probably varies somewhat. 

 The optimum acid concentration for fresh-water fishes in dis- 

 tilled water is about .00005 N H 2 SO 4 . 



4. The distribution of the plankton in the lakes of Wisconsin 

 and New York (Birge and Juday, 'n and '12) shows a very in- 

 teresting correlation with the chemical reaction of the water. 

 There are fewer animals at neutrality than in the slightly alkaline 

 and slightly acid water just above and below the neutral layer. 

 Thus the forms are negative to neutrality. 



5. The neutrality of distilled water is a factor to be considered 

 in its toxicity. 



VII. ACKNOWLEDGMENTS AND BIBLIOGRAPHY. 



I am indebted to Professor V. E. Shelford for many helpful 

 suggestions and numerous courtesies during the working out of 

 the experimental data and preparation of the manuscript. 



