602 NERVOUS SYSTEM 



2. The sneezing centre is related to the trifacial and certain expira- 

 tory muscles. 



3. The centre for coughing is related to the pneumogastric and 

 certain expiratory muscles. 



4. The centre for swallowing is related to the glosso-pharyngeal, the 

 trifacial, the pneumogastric and the muscles of deglutition. 



The bulb also contains (5) the vomiting centre, (6) the glycogenic 

 centre, (7) the dominant sweat-centre, (8) the salivary centre, and (9) 

 the dominant vasomotor centres. 



10. The bulb probably contains inhibitory and accelerator cardiac 

 centres. The fibres of the inhibitory nerves, in the human subject, are 

 contained in the sheath of the pneumogastric. Arising from the bulb, 

 passing into the cord and out of the cord with the communicating 

 branches of the lower cervical and upper dorsal nerves to the sympa- 

 thetic and thence to the cardiac plexus, are the so-called accelerator 

 nerves of the heart. The inhibitory and accelerator nerves are con- 

 nected with the cardiac centre in the bulb. The inhibitory fibres 

 restrain, or inhibit the heart's action, and the action of the accelerator 

 nerves is to increase the number of pulsations. 



n. Respiratory Centres. There are two respiratory centres in the 

 bulb, one on either side of the median line and connected together by 

 commissural fibres. These centres preside over the respiratory move- 

 ments. They do not, however, occupy all that portion of the bulb 

 included between the two planes first indicated by Flourens, but are 

 confined to the gray matter of the lateral tracts, or the intermediary 

 fasciculi. This is shown by the fact that respiration persists in animals 

 after division of the anterior pyramids and the restiform bodies. 

 Nearly all experimenters have found that the spinal cord may be 

 divided below the bulb, and that all the encephalic ganglia above may 

 be removed, respiratory movements still persisting. It is a common 

 thing in vivisection to kill an animal by breaking up the bulb. When 

 this is done there are no struggles and no manifestations of the distress 

 of asphyxia. The respiratory muscles simply cease their action, and the 

 animal loses instantly the sense of want of air. A striking contrast to 

 this is presented when the trachea is tied or when all the respiratory 

 muscles are paralyzed without touching the medulla. 



Under normal conditions the centres on the two sides probably 

 operate through the pneumogastric nerves, and the respiratory move- 

 ments on the two sides are synchronous. That there is a respiratory 

 centre on either side is shown by the experiment of dividing the bulb 

 longitudinally in the median line, the respiratory movements afterward 

 continuing with regularity. If, now, the pneumogastric is divided on 



