REACTION AND RESISTANCE OF FISHES. 249 



care; he considered and seemed to have eliminated the following 

 possible toxic factors: copper, impurities from the glass, low 

 oxygen, ammonia, and carbon dioxide. He found also that 

 NaCl in small concentrations would neutralize the toxicity of 

 the pure water to such an extent that the animals lived almost 

 as well in an .00008 N solution of this salt as in the natural 

 fresh water. The toxicity of pure distilled water, he concluded, 

 is due to the lack of salts in solution. Peters in 1908 performed 

 some very careful experiments to test the effect of pure distilled 

 water upon protozoa. He came to the conclusion that distilled 

 water which contains no salts, and which is changed often enough 

 to prevent their accumulation from the metabolism of the ani- 

 mals, is rapidly toxic to these forms. 



I have gone over the above papers and have found many 

 statements which indicate that the presence of a certain con- 

 centration of hydrogen ion, was beneficial to the animals ex- 

 perimented upon. For instance, Ringer ('83) states that the 

 distilled water which he used killed minnows, on an average, 

 in 4.5 hours. He also says that the distilled water was very 

 faintly acid; so faint was the acidity that he did not rely upon 

 his own judgment but had others make the test also. However, 

 he says, to prove that the acidity was not the cause of the death 

 of the minnows, he took three liters of water and to one added 

 6 drops of 10 per cent, acetic acid, to the next 12 drops and to 

 the third 20 drops. He then placed three minnows in each liter 

 of acid solution. After 24 hours, the minnow r s were "quite 

 natural" and he concluded, therefore, that the acidity could 

 not have been harmful in the case of the distilled water. This 

 conclusion of Ringer's illustrates the attitude taken by most 

 authors with regard to the presence of acid in the water, that is, 

 the acid is looked upon as a detrimental factor, to be considered 

 negatively. So far as I have been able to read, the authors 

 quoted above have taken little consideration of the possibility 

 that the presence of a certain concentration of H or OH ion is 

 essential to the welfare of animals. 



This Ringer does not suggest, even though the minnows in 

 the acid water were well on the way to live as long as any of the 

 animals kept in salt solutions. In this same paper, Ringer notes 



