314 PHYSIOLOGY OF RESPIRATION OF FISHES 



The individual variation of fish of a given species might depend upon 

 the individual variation in the alkaline reserve of the blood. 



These conclusions are further emphasized by FitzGerald's obser- 

 vations (1913, 1915), and recent experiments by Henderson (1919), 

 Haggard and Henderson (1920), and Henderson (1920) on the part 

 played by the alkaline reserve of the blood in the acclimatization to 

 altitude. It might be further suggested that the species of fish 

 having the greatest ability to vary the alkaline reserve of their blood 

 would also have the greatest power to withstand a variation in 

 carbon dioxide tension of the water. The rapidity of the change in 

 the carbon dioxide tension which a fish would be able to withstand 

 would depend upon the rapidity with which it is able to vary the 

 alkaline reserve of its blood. In man (Henderson, 1920) this seems 

 to be a rather slow process. This is a more logical explanation since 

 the carbon dioxide and oxygen tension in the environment of the fish 

 are not so intimately connected as with the air-breathing animals. 

 But as a general rule when the oxygen content of the sea water is 

 low the carbon dioxide is increased (Powers, 1920). However, 

 further experiments are necessary to settle these points. 



In the light of these experiments it is easily seen why Wells (1913) 

 found that high carbon dioxide was more rapidly fatal to fishes than 

 low oxygen and why fishes are able to sense out and detect variations 

 in carbon dioxide tension more easily than the variations in the 

 oxygen tension (Shelford and AUee, 1913). Bayliss (1918) states: 

 " .... if increase in carbon dioxide be prevented, as by 

 respiration of pure nitrogen, a man may become unconscious before 

 experiencing any unpleasant symptoms." 



It is conceivable that the carbon dioxide tension of the water could 

 be raised above the carbon dioxide tension of the tissue capillary 

 blood of the fish. Under this condition the oxyhemoglobin would 

 be reduced to hemoglobin in the capillaries of the gills of the fish 

 rather than the hemoglobin being oxidised to oxyhemoglobin. The 

 fish would then suffer oxygen want more quickly in water with a 

 high carbon dioxide tension and ordinary oxygen tension than in 

 water with a low carbon dioxide tension and a low oxygen tension. 

 Thus the probabilities are that in Wells' experiments the high oxygen 

 tension was not antagonistic to the high carbon dioxide tension, in 



