CHAP, ii.] RESPIRATION. GOT 



venous blood) of the medulla oblongata, is proved by the fact that 

 they fail to make their appearance \vhen the spinal cord has been 

 previously divided below the medulla, though they still occur 

 after those portions of the brain which lie above the medulla have 

 been removed. It is usual to speak of a 'convulsive centre' in 

 the medulla, the stimulation of which gives rise to these con- 

 vulsions ; but if we accept the existence of such a centre we must 

 at the same time admit that it is connected by the closest ties 

 with the normal expiratory division of the respiratory centre, since 

 every intervening step may be observed between a simple slight 

 expiratory movement of normal respiration and the most violent 

 convulsion of asphyxia. An additional proof that these convulsions 

 are carried out by the agency of the medulla is afforded by the fact 

 that convulsions of a wholly similar character are witnessed when 

 the supply of blood to the medulla is suddenly cut off by ligaturing 

 the blood vessels of the head. In this case the nervous centres, 

 being no longer furnished with fresh blood, become rapidly 

 asphyxiated through lack of oxygen, and expiratory convulsions 

 quite similar to those of ordinary asphyxia, and preceded like them 

 by a passing phase of dyspnoea, make their appearance. Similar 

 ' anaemic ' convulsions are seen after a sudden and large loss of 

 blood from the body at large, the medulla being similarly 

 stimulated by the lack of arterial blood. In ordinary fainting, 

 which is loss of consciousness due to an insufficient supply of 

 blood to the brain, the diminution of blood supply is not great 

 enough to produce these convulsions. 



Such violent efforts speedily exhaust the nervous system ; and 

 the convulsions after being maintained for a brief period suddenly 

 cease and are followed by a period of calm. The calm is one of 

 exhaustion ; the pupils, dilated to the utmost, are unaffected by 

 light ; touching the cornea calls forth no movement of the eyelids, 

 and indeed no reflex actions can anywhere be produced by the 

 stimulation of sentient surfaces. All expiratory active movements 

 have ceased ; the muscles of the body are flaccid and quiet ; and 

 though from time to time the respiratory centre gathers sufficient 

 energy to develope respiratory movements, these resemble those of 

 quiet normal breathing, in being, as far as muscular actions are 

 concerned, almost entirely inspiratory. They occur at long inter- 

 vals, like those after section of the vagi ; and like them are deep 

 and slow. The exhausted respiratory centre takes some time to 

 develope an inspiratory explosion; but the impulse when it is 

 generated is proportionately strong. It seems as if the resistance 

 which had in each case to be overcome was considerable, and 

 the effort in consequence, when successful, productive of a large 

 effect. 



Very soon, these inspiratory efforts become less frequent; 

 their rhythm becomes irregular; long pauses, each one of which 

 seems a final one, are succeeded by several somewhat rapidly 



