244 MORRIS M. WELLS. 



mous species, probably would not survive in water which was 

 even faintly acid. Since algae and other phytoplankton forms 

 (Birge and Juday, 'n and '12) may cause a body of water to be- 

 come partially or wholly alkaline, through their ability to dis- 

 sociate the bicarbonates, vegetation in fish waters assumes a 

 line of importance heretofore little considered. The effects 

 of sewage upon the acidity or alkalinity of natural bodies of 

 water must also be reconsidered in the light of its possible in- 

 jurious or beneficial effects due to its chemical reaction. Thus 

 a large number of interesting and important questions suggest 

 themselves. 



The effect of the chemical reaction of the water upon the 

 distribution of organisms promises much room for investigation. 

 There is no doubt but that fishes recognize the difference be- 

 tween very faintly acid or very faintly alkaline, and neutral 

 water. Henderson's work ('13), upon the mechanism which 

 maintains a constant proportion of H and OH ions in the blood 

 of animals, suggests the physiological reason for this extreme 

 sensitiveness of the fishes. It is clear that even very small 

 variations in the proportions of these two ions in the blood of 

 the organism, are of grave importance, and we find in the blood 

 a combination of gases and salts that makes such variations 

 impossible as long as the animal is normal. The blood will main- 

 tain its normal chemical reaction (just on the alkaline side of 

 neutrality) in the face of relatively large changes in the environ- 

 ment, yet we know that the mechanism breaks down when the 

 change is either too great or too long continued (acclimatization 

 is not considered at this time). The hyper-sensitiveness of the 

 animals to the chemical reaction of the water, in the case of aqua- 

 tic organisms, is another important factor in preserving the 

 normal reaction of the blood, as the reactions of the organisms 

 work in a way that causes them to turn back from concentrations 

 of H or OH ion that would be detrimental. The delicacy and 

 accuracy of these reactions are evidenced in the reaction ex- 

 periments which have been discussed in the preceding pages. 



The physiological effect of the acid, neutral, and alkaline 

 water upon the organism very probably has to do with decrease 

 or increase in the permeability of the exposed tissue cells (es- 



