ANATOMY AND PHYSIOLOGY OF THE NERVOUS SYSTEM. 



erves and muscles of forced expiration (normal expiration is aceom- 

 lished by reason of the elasticity of the thoracic case). 



Experimentally it is observed that exciting the vagus nerves or 

 heir central stumps provokes very deep inspirations until the thorax 

 stops in the inspiratory movement. 



Stimulating the superior laryngeal nerves or their central 

 stumps provokes violent and forced expirations until the thorax stops 

 in the expiratory movement. 



It is said that when a lesion affects the bilateral respiratory 

 center there follows immediate sus- 

 pension of breathing, and, there- 

 fore, death. 



The medulla oblongata is a 

 moderating center of the move- 

 ments of the heart. By irritating 

 the medulla near the originating 

 nucleus of the vagus nerve there is 

 used a stoppage of the cardiac 

 movements. The heart first slack- 

 ens its systole and afterward stops 

 in diastole. The medulla exercises 

 this moderating action upon the 

 heart through the vagus nerve as a 

 medium. Some of its centrifugal 

 fibers put themselves in relation 

 with its inhibitory ganglia. Hence, 

 moderation and suspension of the 



heart movements is obtained by irritating the peripheral stump of the 

 vagus in the neck. According to Traube, the normal stimulus, capable 

 exciting this moderating action, is the accumulation of C0 2 in the 

 ood. 



In the medulla is found this moderating center, which is antago- 

 istic to that other center seated in the medulla oblongata: the 

 lerator center of the heart. 



The medulla contains the principal vasomotor center, which is of 

 e utmost importance to the economy. This general vasomotor 

 nter in the medulla may become stimulated directly from the brain. 

 short, an emotion or irritation to the cerebral cortex readily 

 gs on ischaemia or hypersemia either in the skin or in the internal 

 gans. Thus, there may be pallor from fear or diarrhoea from 

 ight. 



Fig. 273. Floor of Fourth Ventricle 

 of Rabbit. (HEDON.) 



Puncture at a, a little above the Dib of the 

 calamus, produces diabetes. Puncture at 

 6 produces polyuria without glycosuria. 



