1094 



PHYSIOLOGY 



pulmonary ventilation is possible, by increass of depth of respiration alone, 

 is not so great as in a normal animal. Moreover, since no quickening of 

 respiration takes place, the increased ventilation rapidly becomes inadequate 

 for the maintenance of the normal alveolar carbon dioxide tension. In the 



FIG. 514. Effect of 10-6 per cent. C0 2 in a mixture containing 23'3 per cent. 2 on a " 

 rabbit with both vagi divided. The gas was administered between the arrows. 

 Zero line of blood-pressure is 32 mm. below bottom of tracing. Compare this 

 figure with Fig. 505, p. 1081. (F. H. SCOTT.) 



following Table the total amounts of pulmonary ventilation obtained on 

 administration of mixtures containing carbon dioxide to a rabbit before 

 and after section of the vagi are compared. 



Whether we assume that the prevailing impulses travelling up the 

 vagi are purely inhibitory or are both inhibitory and augmentor, the re- 

 sultant effect, by reining in the activity of the centre, is to economise its 

 energy and the energy of the respiratory muscles. The result of the vagal 

 impulses will therefore be to increase the excitability of the respiratory 

 centre and make it more susceptible to slight changes in the carbon dioxide 

 tension of the blood, while maintaining a sufficient margin of energy to 



