Respiratory Functions of Body Fluids 



317 



that addition of COo to a closed vessel containing trout blood might cause the 

 appearance of a bubble of oxygen.^' When the COo tension is increased from 

 1 to 11 mm. the ti/2 sut of a brook trout rises by 30 mm., whereas in man an 

 increase of 10 mm. in CO2 causes a rise in lyn sat of about 3.3 mm. A small 

 increase in COo may force Hsh with a low O2 affinity into water of very high 

 oxygen, whereas in fish with low tensions of loading the COo effect is less 

 significant (Fig. 71, Table 56). Among fresh-water fish the ti/2 sat of the 

 catfish, carp, and bowfin is not raised above 10 mm. O2 by 10 mm. CO2, 

 whereas the t]/2 sat of the sucker and of each of three species of trout is raised 

 above 35 mm. O2. Sensitive marine fish are toadfish, mackerel, and sea robin; 



TizSAT 



TEMPERATURE 



Fig. 72. Effects of temperature on the O2 tension for half saturation of blood. • man, 

 Brown and HilP'; O marmot, Enders''; X goose, + pigeon, A duck, Wasd and 

 Leiner.^^* 



elasmobranchs are less affected by CO2, and for the skate (Raja ocellata) the 

 ti/2 sat is relatively constant over a wide range of CO2 tensions.-'' 



The response of the Oo dissociation curve to CO2 is similar, whether the 

 red cells are intact or hemolyzed, in the trout, sea robin, and Atlantic salmon. 

 In other fish, such as the carp, sucker, tautog, and toadfish, the effect of CO2 

 is less on hemolvzed blood than on blood with the cells intact. Apparently 

 the hemoglobin of the latter group of fish is made up of several oxygen-com- 

 bining components which combine with different amounts of oxygen at a 

 given tension while in the cells.^-^*' When the blood is hemolyzed the oxygen 

 dissociation curve at a given CO2 tension lies to the left of that of whole blood. 



Willmer^^^ has studied the bloods of several fish in tropical South America. 

 Those which live in active rivers have hemoglobin which is sensitive to CO2 



