xiii RESPIRATORY RHYTHM 467 



In order to study the reciprocal and opposite action of the 

 two respiratory phases (inspiration and expiration) he uses a pro- 

 longed contraction of the rabbit's diaphragm, produced by direct 

 faradisation of the diaphragm itself, exposed by means of a large 

 aperture in the thorax, artificial respiration being temporarily 

 suspended. 



He noted that when the contraction of the diaphragm had 

 hardly begun the nostrils became fully dilated, as in every normal 

 act of inspiration. Almost at once, however, if the tetanic con- 

 traction of the diaphragm was kept up, the nostrils became con- 

 stricted nearly to complete closure, and remained in that position 

 during the whole period of the contraction. 



On bilateral section of the phrenic in the neck this reflex 

 disappeared completely. Accordingly it originates in the con- 

 tracted diaphragm, and determines secondarily the closure of the 

 nostrils, which, as we have seen above, is a purely expiratory act. 

 " Hence," concludes Baglioni, " we have here a respiratory reflex of 

 essentially the same character as those respiratory reflexes on 

 which Hering and Breuer based their theory of auto-regulation, 

 but with this difference, that here the afferent impulse travels not 

 by the pulmonary vagus but by the centripetal fibres of the 

 phrenic." 



Recently (1907) Baglioni has emphasised the importance he 

 attaches to these respiratory reflexes, which must be determined 

 by the two respiratory phases, the iiispiratory muscles by their 

 contraction exciting the centres, and thus reflexly determining the 

 contraction of the expiratory muscles, and vice versa. 



VIII. From all that has been said above, we may deduce the 

 following conclusions, which are of fundamental importance to the 

 theory of respiratory innervation : 



(a) Normal respiratory rhythm (eupnoea}, which is the best 

 adapted to produce with minimum expenditure of energy that 

 degree of pulmonary ventilation which suffices for the chemical 

 needs of the organism, is essentially conditioned by the activity of 

 the centripetal fibres of the pulmonary branches of the vagus, 

 which are in direct relation with the bulbar centres. It persists 

 after the separation of the spinal bulb from the brain. 



(H) It is the function of the pulmonary fibres of the vagus to 

 maintain the lungs in that state of average dilatation whicli 

 obtains when all the respiratory muscles are inactive. They are 

 excited on the one hand by the rise of pulmonary pressure and of 

 the inspiratory dilatation of the lungs, which reflexly determine 

 the act of expiration, just as the fall of pulmonary pressure and 

 the expiratory retraction of the lungs reflexly determine the act 

 of inspiration. 



(c) When the auto-regulation of respiration by means of the 

 vagi is suppressed, an abnormal type of respiratory rhythm appears, 



