EDWIN B. POWERS 313 



stopped tightly to exclude air than those not so injected. He also 

 found that when the fish were injected with m/250 to m/500 solution 

 of acetic acid, they did not live as long as the control fish. From 

 these experiments Birge and Juday (1911) suggested that **if a fish 

 possessed the power to alter the composition of its blood somewhat, 

 it would be able to adapt itself to water which contains only a com- 

 paratively small amount of dissolved oxygen." Might it not be 

 possible in these experiments, since the oxygen tension was lowered 

 by the respiration of the fish, that the differences in survival time of 

 the fish were due to the variations in their abilities to absorb oxygen 

 from the sea water at low oxygen tension under the conditions of the 

 experiment? That is, the fish whose blood was best adapted to 

 absorb oxygen at low tension at the particular carbon dioxide tension 

 of the experiment would survive longest. This ability would perhaps 

 depend upon the alkaline reserve of the blood of the fish. That is, 

 if the hemoglobin of the blood of all the fish of a given species had 

 the same optimmn pH to carry oxygen, the fish would be able to extract 

 oxygen from the water at low oxygen tension in the direct order of the 

 alkaline reserve of the blood at a carbon dioxide tension higher than 

 the optimum and in the reverse order of the alkaline reserve in a 

 carbon dioxide tension below the optimum. In these experiments 

 the carbon dioxide tension would tend to increase above the optimum 

 for the absorption of oxygen at low tension since ordinary sea water 

 was used and, as the oxygen was absorbed by the confined fish, carbon 

 dioxide would be given off .- 



The experiments recorded in the figures show that the species of 

 fish tested have an optimum pH of more or less narrow or wide 

 range for absorbing oxygen from the sea water at low oxygen tension. 

 The limiting factor is perhaps the carbon dioxide tension of the sea 

 water. The pH of the sea water with a given alkaline reserve is de- 

 pendent upon the carbon dioxide tension (Henderson and Cohn, 1916, 

 and McClendon, 1917). The optimum carbon dioxide tension of 

 the sea water for a species of fish as suggested above would perhaps 

 depend upon the alkaline reserve and the optimum pH of its blood. 



* The author has performed experiments which give strong evidence for this 

 probability, which are reserved for further publication. 



