MECHANICS OF THE RESPIRATORY MOVEMENTS 1097 



(Brodie and Dixon). By both these methods it has been shown that 

 stimulation of the peripheral end of either vagus causes constriction of the 



FIG. 501. Tracings of blood pressure (middle curve) and of intra-tracheal pressure 

 (upper curve) taken by Einthoven's differential manometer. Between Q and Q' 

 the peripheral end of one vagus was stimulated. Time marking = seconds. 



bronchioles (vide Figs. 502 and 503). As a rule there is little tonic action of 

 the vagi, section of both vagi leaving the respiratory pressure curve unaltered 

 or lowering it slightly by 2 to 10 mm. H 2 0. It is very easy to bring about 



FIG. 502. Tracings of the volume changes of the lung, with constant variations of 

 tracheal pressure. (BfiODiE and Dixcxs.) T. P. tracheal pressure. L.V. lung 

 volume, B.P. blood pressure (Zero B.P. 17 mm. below time marker). Showing 

 constriction of bronchial musculature as a result of vagus excitation. 



a vagus tonus by allowing the animal to inhale air containing 3 to 4 per 

 cent, carbon dioxide. A peripheral tonus may also be produced by ad- 

 ministration of muscarine or pilocarpine. In the latter case Brodie -and 

 Dixon have shown that stimulation of the vagus may cause relaxation 



