318 



Comparative Animal Physiology 



(Table 56). In one which is found near waterfalls (the paku), addition of 

 25 mm. COo decreased the oxygen saturation by 48 per cent; in three other 

 river fish a similar amount of COo reduced the oxygenation by about 25 per 

 cent. In three species inhabiting sluggish marshy ponds, where the water pH 

 varied from 3.8 to 5.0, the CO2 effect was much less: 12-13 per cent reduction 

 in saturation by 25 mm. CO2 in two of them and only 7 per cent reduction in 

 the electric eel. The U/2 sat in these sluggish-water fish is similar to the ti/o 

 sat in those from fast waters, but the blood of the former is tolerant of higher 

 C0> in the water. 



TlZSAT 

 'nAM HO 



50 



40 



30- 



I- '0 



20- ^ 



LIMULUS 

 PHASCOLOSOMA 



10 



20 



30 



40 



50 



TEMPERATURE C 



Fig. 73. Effects of temperature on the Oo tension for half saturation of blood. • Helix, 

 Wolvekamp and Kersten""; ® Limnliis, X Loligo, Redfield and Ingalls^^''; A Phascoloso- 

 ma, Florkin*"; + Urechis, Redfield and Florkin.'"' 



The blood of some fish is also very sensitive to changes in temperature. A 

 rise in temperature acts like CO. to lower the Oo affinity. Figure 74 shows 

 that m the trout a rise in temperature of a few degrees raises the unloading 

 tension significantly. In three different species of trout the t,/o ,„t rises about 

 1 mm. I Ig ol oxygen partial pressure per degree centigrade. At higher tempera- 

 tures the amount of oxygen dissolved in water is also diminished. The effect 

 of temperature on the availability of oxygen is undoubtedlv a factor in the 



