THE BRAIN. -i-iS 



generates within itself the nervous stimulus to respiration, indepen- 

 dently of external impressions. The immediate cause of its action is 

 attributed by Flint to a deficiency of oxygenated blood in its capillary 

 vessels, by which it is excited to momentary activity. The author sus- 

 tains this view by the result of experiments on animals, in which invol- 

 untary movements of respiration were excited by cutting off the supply 

 of arterial blood from the medulla and other parts of the encephalon. 

 But both these authors agree in considering the medulla as in some 

 way the indispensable nervous centre for respiration. 



An irregularity in the movements of respiration is, accordingly, one 

 of the most threatening symptoms in affections of the brain. Cerebral 

 apoplexy at the surface of the hemispheres, in the lateral ventricles, or 

 in the cerebral ganglia, is seldom immediately fatal, however extensive 

 the injury. But when occurring in the medulla oblongata or its im- 

 mediate neighborhood, it produces death instantaneously by the same 

 mechanism as where this part is destroyed by experiment in animals. 

 When the medulla is implicated, in man, by progressive disease or by 

 failure of its nervous functions, the respiratory movements first affected 

 are those of the face, while those of the chest and abdomen go on for a, 

 time as usual. The cheeks are drawn in with every inspiration and 

 puffed out with every expiration, the nostrils sometimes participating 

 in these abnormal movements. A still more dangerous symptom, which 

 frequently precedes death, is an irregular and hesitating respiration, 

 usually noticeable after the remaining cerebral functions have been 

 already impaired. These phenomena depend on the connection between 

 respiration and the medulla as a nervous centre. 



Deglutition is also under the control of the medulla. Mastication 

 of the food, and its transfer by the tongue to the entrance of the fauces, 

 are voluntary actions, which may be continued or arrested at will. But 

 when the food has passed from the mouth into the pharynx, the pro- 

 cess of deglutition, by which it is carried down into the stomach, is 

 reflex and involuntary. Once commenced, it cannot be arrested by 

 the will, as it consists of muscular contractions following each other in 

 undeviating succession, and receiving their impulse from the medulla 

 oblongata. In the experiments of Flourens and Longet, fowls and 

 pigeons, after removal of the cerebral hemispheres, never picked up 

 their food spontaneously, nor even swallowed it w T hen placed in the 

 mouth at the end of the beak ; but if carried backward into the pharynx, 

 it was at once embraced by the muscular walls of this organ, and car- 

 ried into the stomach by a continuous movement of deglutition. This 

 movement includes, not only the associated contraction of the pharynx 

 and oesophagus, but also the stoppage of respiration and closure of the 

 glottis, by which the food is prevented from passing into the larynx. 

 According to Yulpian, after all parts of the brain have been removed, 

 in cats or guinea-pi<rs, excepting the medulla, swallowing may still be 

 accomplished by reflex action ; but it becomes impossible as soon as 

 this part is removed or seriously injured. The necessary muscular 



