CHAP, ii.] RESPIRATION. 473 



When an intercostal nerve is cut, no active respiratory 

 movements are seen in the intercostal muscles of the corre- 

 sponding space, and when the spinal cord is divided below the 

 origin of the seventh cervical spinal nerve, that is U-low tin? 

 exits of the roots of the phrenic nerves, costal respiration 

 ceases, though the diaphragm continues to act, and that with 

 increased vigour. When the cord is divided just below the 

 spinal bulb, all thoracic movements cease, but the respiratory 

 actions of the nostrils and glottis still continue. These how- 

 ever disappear when the facial and recurrent laryngeal nerves 

 are divided. We have already stated that after removal of 

 the brain above the spinal bulb, respiration still continues very 

 much as usual, the modifications which ensue from the loss of 

 the brain being unessential. Hence, putting all these facts 

 together, it is clear that the respiratory movements are, as we 

 suggested, brought about by coordinated impulses which, de- 

 veloped in the central nervous system and starting in the first 

 instance in the spinal bulb, find their way along the several 

 efferent nerves. The proof is completed by the fact that tin- 

 removal of or extensive injury to the spinal bulb alone is, save 

 in exceptional cases which we will discuss presently, at once 

 followed by the cessation of all respiratory movements, even 

 though the rest of the nervous system including every muscle 

 and every nerve concerned be left intact. Nay more, if only 

 a small portion of the spinal bulb, a tract whose limits have 

 not been clearly defined, but which may be described as 1 

 below the vaso-motor centre in the immediate neighbourhood 

 of the nuclei of the vagus nerves, be removed or injured, respi- 

 ration ceases, and death at once ensues. Hence this portion of 

 the nervous system was called by Flourens the vital knot, or 

 ganglion of life, ' nceud vital. 1 We shall speak of it as the 

 respiratory centre. 



293. The nature of this centre must be exceedingly com- 

 plex ; for while even in ordinary respiration it gives rise to a 

 whole group of coordinate nervous impulses of inspiration 

 followed in due sequence by a smaller but still coordinate 

 group of expiratory impulses of an antagonistic nature, in 

 laboured respiration fresh and larger impulses are generated, 

 though still in coordination with the normal ones, the expira- 

 tory events being especially augmented ; and in the cases of 

 more extreme dyspnoea and asphyxia impulses overflow, so to 

 speak, from it in all directions, though only gradually losing 

 their coordination, until almost every muscle in the body is 

 thrown into contractions. 



We must not however conceive of this centre as one of sueh 

 a kind that the impulses leave it fully coordinated and equipped 

 so that nothing remains for them but to travel, unchanged, 

 along the several efferent nerve-fibres to their several muscular 



