546 



VETERINARY PHYSIOLOGY 



The tissues must be able to take up the oxygen they 

 require from a wide range of pressure in the blood. 



CYAN 05 15 



+H- 



++ 



PER CENT 10 



Fig. 222. — To show the relationship between the saturation or unsaturation 

 with oxygen of arterial and venous blood, with variations in the 

 unsaturation of arterial blood from 5 to 50 per cent., in cases of 

 pneumonia, with different degrees of cyanosis. (Stadie.) 



Such results cannot fail to raise the question of the 

 beneficial effects of administering oxygen in pneumonia in order 

 to increase the supply to the tissues. 



When a stagnation of blood in the capillaries occurs, it is 

 very probable that the removal of oxygen is so complete that 

 a true oxygen starvation of the tissues exists. 



(1) The tissue elements are always taking up oxygen from 

 the tissue fluids, because of the very low tension of oxygen in 

 the protoplasm. 



(2) As a result of this, the oxygen pressure in the fluids 

 falls and becomes lower than the oxygen pressure of the blood 

 plasma, and thus the gas passes from the blood, through the 

 capillary walls, to the fluids. 



(3) As a result of the w^ithdrawal of oxygen from the plasma, 

 the partial pressure round the erythrocytes is diminished, 

 a dissociation of oxyhsemoglobin takes place, and the oxygen 

 passes out into the plasma, leaving some of the haemoglobin in 

 the erythrocytes in a reduced condition. 



2. Carbon Dioxide. — The tissues are constantly producing 

 carbon dioxide, so that it is at a high tension in them — about 

 60 mm. Hg. In the blood, as already indicated, it is partly 

 dissolved and partly combined with sodium as the bicarbonate. 

 Possibly it is partly combined with the proteins of the plasma, 

 and probably in part with the globin of haemoglobin (p. 496). It 



