EDWIN B. POWERS 307 



fluence of acids, alkalies, and potassium salts, and Loeb and Northrop 

 (1917) that the mortality curve of the fruit fly (Drosophila) under the 

 influence of food and temperature are probability curves. The 

 probable cause of the variations in the ability of different individual 

 fish of the same species to absorb oxygen from the medium at low 

 oxygen pressure at a given hydrogen ion concentration and tempera- 

 ture will be taken up later. 

 The figures are graphic representations of the experimental data. 



The Ability of Fishes to Extract Oxygen from the Sea Water at Different 

 Hydrogen Ion Concentrations. 



(a) The Cunner {Tautogolabrus adspersusWalhsLXxm). — The cunner 

 was able to extract oxygen from the sea water down to approximately 

 0.25 cc. per liter before asphyxiation at all hydrogen ion concentrations 

 up to about 6.5 pH. From this point on there seems to be a rapid 

 loss in the ability of this fish to extract oxygen from the sea water 

 at low oxygen pressure (Fig. 1). 



(6) The Butter-Fish (Poronotus triacanthus Peck). — Fig. 2 shows 

 that the butter-fish was not able to extract the oxygen from the sea 

 water at quite as low a level as the cunner. The general trend of the 

 curve indicates that the butter-fish is able to absorb oxygen at the 

 lowest concentrations at a pH of about 7.6 to 7.8. This was shown 

 even more strikingly when individuals were considered, the lowest 

 point at which oxygen was absorbed being 0.36 cc. per liter at 7.58 pH 

 and 0.35 cc. per liter at 7.57 pH. There was a slight falling off in the 

 power to extract the oxygen at low concentrations, as the hydrogen 

 ion concentration of the sea water was lowered from a pH of about 

 7.6 or 7.8 to 9.0. The falling off was much more rapid when the 

 hydrogen ion concentration was increased from a pH of about 7.6 

 to 6.3, being most rapid from 7.1 to6.35. At the higher hydrogen ion 

 concentrations but very little of the oxygen had been absorbed 

 before asphyxiation took place. 



(c) The Mackerel (Scomber scombrus L.). — There was only a slight 

 variation in the ability of the mackerel to extract oxygen from the 

 sea water at low tension from about 7.7 pH to about 8.2 pH within 

 an optimum at about 8.0 pH. There was a more or less falling off in 



