FUNCTIONS OF BLOOD 



103 



gen concentrations, while in tropical swamps the low oxygen 

 may be further complicated by rather high C0 2 tensions. 

 The haemoglobins of many animals show characteristic adapta- 

 tions to these conditions. The blood of the carp, pike, and 

 eel was found to have at 15°C a h of about 10 mm and a /„ at 

 a very low C0 2 tension (0.3 mm) of 2-3 mm (Krogh and 



Fig. 59. 



eo 40 60 ao /oo teo 



Part/a/ Pressure of Oxyyen /n mm /iy. 



m fio 



Oxygen dissociation curves of carp blood at 15°C and different CO,' 

 tensions. (Black and Irving.) 



Leitch, 1919; Black and Irving, 1937). This would make the 

 transfer of oxygen to the tissues extremely difficult were it not 

 that the C0 2 effect is very large and may raise the t u to 6 mm 

 (at 7.5 mm C0 2 ) and probably beyond. Black and Irving 

 found a t u at 18-20 mm C0 2 tension of not less than 25 mm 

 (Fig. 59). These adaptations enable the fishes to live in very 

 poor water which would be rapidly fatal, e.g., to trout. 



Certain invertebrates possessing haemoglobin utilize the 

 pigment only at low oxygen tensions, while diffusion and trans- 

 port in simple solution is sufficient at higher tensions. This 

 point is brought out when the haemoglobin is put out of func- 

 tion by exposing the animals to a low concentration of carbon 



