348 MANUAL OF PHYSIOLOGY. 



stantly at work modifying the respiratory rhythm. We may 

 assume that the slow, deep respirations which follow section of 

 the vagi are caused by the unregulated automatic action of the 



FIG. 154. 



Diagram of the Nervous Mechanisms of Respiration. (After Fick ) sc. Centre for 

 inspiratory movements, from which pass efferent channels, represented by the continu- 

 ous white line (o) to the inspiratory muscles represented by the diaphragm (D). EC. 

 Centre for expiratory movements, from which efferent channels (p) pass down the cord 

 to the muscles of expiration, represented by the abdominal muscles (A). To both these 

 centres affrent impulses come (1) from the cerebral centres (a, b, c, d) to check or excite 

 activity. These voluntary impulses may be called afferent as far as the respiratory cen- 

 tres are concerned. From (2) the cutaneous surface, and (3) the nose, impulses (e,f, g) 

 arrive, which modify the action of the inspiratory centre. From the (4) larynx (G) 

 come checking impulses (h) to the inspiratory, and exciting impulses (i) to the expiratory 

 centre; and, finally, (5) from the lungs come both exciting and inhibiting impulses (k, I. 

 m, n) to both the expiratory and inspiratory centres, and by these channels the rhythm 

 of ordinary breathing is regulated. 



