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A MANUAL OF VETERINARY PHYSIOLOGY 



The process is termed dissociation ; this may be defined as 

 the tendency which certain gases have to leave the substances 

 with which they are united when the surrounding pressure 

 becomes reduced. In the animal body it is not confined to the 

 combination of oxygen with haemoglobin ; the same process is 

 at work in assisting to liberate the carbon dioxide in the lungs 

 from the substances with which this is chemically combined. 



When sufficient haemoglobin exists in ioo volumes of blood to 

 carry 20 c.c. of oxygen, the haemoglobin is said to be saturated. 

 If only half the amount exists, then only 10 c.c. of oxygen are 



3CC. 



10 20 30 40 SO 60 70 60 90 100 HO 120 130 140 ISO 



Fig. 49. — Curves of Dissociation of Oxygen for Horse's Blood (B) and 

 Dog's Hemoglobin Solution (H) at 38 C. (Bohr). 



Along the horizontal axis are plotted the partial pressures (numbers below the 

 curve) of oxygen in air, to which a solution of haemoglobin was exposed. 

 The corresponding percentages of oxygen are given above the curve. Along 

 the vertical axis is plotted the percentage saturation of the haemoglobin with 

 oxygen. Thus, on exposure to an atmosphere in which oxygen existed to 

 the extent of 1 per cent., corresponding to a partial pressure of y6 mm. of 

 mercury, the haemoglobin took up about 75 per cent, of the amount of oxygen 

 required to saturate it. When the oxygen was present in the atmosphere 

 to the amount of about 10 per cent., corresponding to a partial pressure of 

 76 mm. of mercury, the quantity taken up by the haemoglobin was about 

 96 per cent, of that required for saturation. 



in chemical combination in ioo c.c. of blood, and the percentage 

 of saturation is 50. Two dissociation curves are given in 

 Fig. 49, one for horse's blood, and one for a solution of dog's 

 haemoglobin. The curve illustrates the blood-pump experiment 

 previously described. At 150 mm. pressure of o. ygen, corre- 

 sponding to atmospheric pressure, the blood is saturated with 

 oxygen. It contains 20 c.c. in each ioojvolumes. In horse's 

 blood there is no attempt at dissociation] until the pressure is 

 reduced to 50 mm., and by the time it has fallen to 14 mm. 

 half the total amount of oxygen united to the haemoglobin has 



