EDWIN B. POWERS 315 



the true sense of the word, but that the oxygen tension was below 

 on the one hand, and on the other it was above the tension at which 

 hemoglobin could be oxidised to oxyhemoglobin in the presence of 

 a high carbon dioxide tension. 



SUMMARY. 



1. The ability of marine fishes to absorb oxygen at low tension 

 from the sea water is more or less dependent upon the hydrogen ion 

 concentration of the water. 



2. The ability of fishes to withstand wide variations-in the range 

 of hydrogen ion concentration of the sea water can be correlated with 

 their habitats. The fishes that are most resistant to a wide varia- 

 tion in the hydrogen ion concentration are most cosmopolitan in their 

 habitat. Those that are least resistant to a variation in the hydrogen 

 ion concentration are the most restricted in their range of habitat. 



3. There is a close correlation between the optimum condition of 

 the sea water for the absorption of oxygen at low tension by the 

 herring (Clupea pallasii), the condition of the sea water to which they 

 react positive and that in which they are found most abundantly. 



4. It is suggested that the variation in the ability to absorb oxygen 

 at low tension at a given pH of individuals of a species is dependent 

 upon the alkaline reserve of the blood of the individual fish. 



The author wishes to thank Professor Frank R. Lillie, Director, 

 and Mr. G. M. Gray, Curator, of the Marine Biological Laboratory, 

 and Professor T. C. Frye, Director of the Puget Sound Biological 

 Station, for rooms, equipments, and materials for this work, and for 

 many courtesies during its progress. The author wishes further to 

 thank Professor Jacques Loeb for suggestions in the presentation of 

 data, and Dean R. A. Lyman for reading manuscript. 



BIBLIOGRAPHY. 



Barcroft, J., The respiratory function of the blood, Cambridge, 1914. 



Barcroft, J., and Hill, A. V., The nature of oxyha;moglobin, with a note on its 



molecular weight, /. Physiol., 1909, xxxix, 411. 

 Bayliss, W. M., Principles of general physiology, London, New York, Bombay, 



Calcutta and Madras, 1918. 



