1881.] On Inhibitory Excitation in the Medulla Oblongata. 29 



II. The second motor irritation is effective only when the contraction 

 following the first has passed. 



The anatomical tracts, along which this inhibition is conducted, we 

 have found to be the ramifications of the ninth pair of cranial nerves, 

 the Nn. Glossopharyngei. 



III. If the trunk of the glossopharyngeus is irritated, no movement of 

 deglutition results, in spite of the strongest excitation to deglutition, pro- 

 duced by filling of the pharynx with fluid, or by stimulation of the Nn. 

 laryngei superiores. Both the first reflex act of swallowing and the 

 oesophageal contraction are for the time in abeyance. 



IV". If the pharyngeal branches only are irritated, then the inhibitory 

 phenomenon appears in the cervical or in the thoracic portion of the 

 oesophagus. 



The pharyngeal branches of the 1ST. Glossopharyngeus are not un- 

 frequently distributed in company with the pharyngeal branches of 

 the N. vagus, so that as a complete anatomical separation of the ninth 

 and tenth nerve pairs cannot be effected ; neither can a physiological. 



V. If the N. glossopharyngeus be cut through, the oesophagus falls into 

 tonic spasm, which may last longer than one day. 



It was in continuation of these researches, that the following new 

 and noteworthy observations were made. 



The excitations, which reach their centre in the medulla oblongata 

 through the N. glossopharyngeus, exert an inhibitory influence, not 

 only on the origins of those vagus fibres which supply the oesophagus, 

 but also on the ends of the vagus fibres which excite the movements 

 of respiration and restrain those of the heart. Lastly, the inhibitory 

 influences extend also to the centre in the medulla regulating the 

 blood-vessels. This can be shown in normal living man. One can, 

 by swallowing, easily observe the following : — 



I. During each act of swallowing the pulse frequency increases. 



II. During a series of acts the need of respiration decreases. 



III. During each act of swallowing the blood pressure falls in the 

 aortic system. 



This remarkable proposition, therefore follows : that excitations, 

 which are conveyed to the centre along the tracts of the inhibitory nerves, 

 extend in the character of inhibitions to neighbouring centres. 



Continued researches on the operation of these newly discovered 

 inhibitory nerves promise specially interesting disclosures, for this 

 reason, that they can be set into activity through normal excitations, 

 voluntarily produced, while the observations on the working of the 

 N". vagus, the chief representative of the inhibitory nerves, can be 

 performed only by means of artificial irritation, whose correspondence 

 with natural irritation has by no means been admitted by all. 



