XXI.] THE COLOUB OF BLOOD. RESPIRATION. 227 



3. The colour of venous and arterial blood in the 

 living animal, and its dependence on the pre- 

 sence of oxygen in the lungs. 



4. The respiratory function of the pneumogastric. 



5. The action of the respiratory centre. 



6. The effect of arterial and venous blood on the 

 irritability of muscular tissue. 



7. The phenomena of asphyxia. 



15—2 



