494 



VETERINARY PHYSIOLOGY 



Further increasing the proportion and pressure of oxygen 

 in the air brings about only a slightly increased taking 



up. 



Conversely, if Hb saturated with oxygen is exposed to 

 lower and lower pressures of the gas, it gives up its oxygen 

 slowly till a pressure of 30 mm. Hg is reached and then 

 more rapidly. 



This is shown in fig. 200. 



In blood the curve given is different because of the 



Fig. '201. Dissociation curves of oxyhitmoglobin to show the influence of 



" temperature i., at 16' ; ii., at 25' ; iii., at 32' ; iv., at 38' ; and v., at 

 49' C. Oxygen pressure along abscissa percentage of reduced htemoglobin 

 on vertical line. 



presence of CO.2 and of electrolytes. The taking up of 

 oxygen rises rapidly to 50 mm. Hg, equivalent to 10 per 

 cent, of oxygen in the air, when the haemoglobin is saturated 

 to about 80 per cent. The giving off takes place in the same 

 ratio (fig. 200). 



This association of Hb and O2 and the dissociation are 

 modified by — 



1st Temperature. — Fig. 201 gives the results at iv. 

 about the temperature of the body. If the temperature 



