168 PHYSIOLOGY CHAP- 



mechanism of the swallowing reflex, which is effected by way of 

 the trigeminal. 



As regards the glosso-pharyngeal nerve, both Schiff (1867), 

 and Waller and Prevost found that swallowing was never excited 

 by its stimulation, and concluded that it does not contribute in 

 any way (at least in rabbits) to the reflex phenomena of deglu- 

 tition. Schiff also noted that the division of those nerves in the 

 same animals produced no disturbance of deglutition. It was left 

 for Kronecker and Meltzer (1883) to discover that the glosso- 

 pharyngeal must be regarded as a nerve which reflexly inhibits 

 the swallowing movements. In order to bring out this fact 

 Wassilieff performed the following experiment on rabbits. When, 

 after lateral exposure of the superior laryngeals and glosso- 

 pharyngeals, the former alone are excited, movements of swallow- 

 ing are performed; when the latter are simultaneously excited 

 with weak induction currents the phases of deglutition occur 

 irregularly and are much delayed ; when, lastly, they are stimu- 

 lated with strong currents, the effect of the superior laryngeals is 

 altogether abolished. 



The inferior laryngeals or recurrent nerves also contain centri- 

 petal fibres which are capable of exciting the reflexes of deglutition. 

 This fact, as already surmised by Valentin (1846), and by Waller 

 and Prevost (1870), was fully elucidated by Kronecker and 

 Liischer (1897). They found in a series of experiments on rabbits 

 that the recurrens sends four branches to the cervical part of the 

 oesophagus, the lowest of which innervates the upper part of the 

 thoracic oesophagus also (Fig. 57), and that when the peripheral 

 trunk of one of these filaments is excited even with weak currents, 

 a tetanic contraction occurs exclusively in that segment of the 

 oesophagus in which it ramifies (Fig. 57). When, on the contrary, 

 the whole trunk of the recurrens is excited, the entire cervical 

 part of the oesophagus contracts simultaneously. The peristaltic 

 form of the oesophageal movement that takes place in deglutition 

 must accordingly depend on a delay in the excitation which 

 descends to the three branches of the recurrens in succession from 

 the nerve centre. This agrees with Mosso's earlier and important 

 observation (1873), to the effect that the peristaltic wave of the 

 oesophagus is not arrested in swallowing by ligation, nor by section, 

 nor by extirpation of a quarter of its length ; the wave continues 

 to be propagated from the upper to the lower segments. It ceases 

 only after division of the oesophageal nerves. This fact shows 

 that the peristaltic wave of the oesophagus is not a local pheno- 

 menon propagated from tract to tract by the muscular coat, as in 

 the intestine ; but that it results from the nerve impulses that 

 descend successively by the three branches of the oesophagus from 

 the nerve centres. 



Liischer further noted that stimulation of the central trunk 



