DEGLUTITION. 197 



necessary to the protection of the air-passages from the en- 

 trance of solids or liquids. 



Longet justly attaches great importance to the exquisite 

 sensibility of the top of the larynx in preventing the entrance 

 of foreign substances. His experiments of dividing all the 

 nervous filaments distributed to the intrinsic muscles show 

 that their action is not essential. But on division of 

 the superior laryngeal, the nerve which gives sensibility to 

 the parts, he found that liquids occasionally passed in small 

 quantity into the trachea. This is attributed to the want 

 of sensibility in the mucous membrane above the glottis: 

 " for the animal is not aware in time of the presence of liquid 

 which may accidentally get into the supra-laryngeal cavity, 

 the occlusion of the glottis is sometimes too tardy and does 

 not take place until after the passage of the liquid ; or, again, 

 the animal, instead of then making a sudden expiration, 

 makes an unseasonable inspiration which facilitates the in- 

 troduction of the foreign substance into the air-passages, and 

 the cough does not take place until this is already in contact 

 with the tracheal or bronchial mucous membrane." ! 



These experiments beautifully illustrate the conservative 



1 Op. cit.j tome i., p. 110. The two most elaborate and interesting articles 

 on the occlusion of the glottis in deglutition are those of Magendie and Longet. 

 The memoir of Magendie was presented to the first class of the Institute of France 

 in March, 1813. It contains the first experiments on record concerning the uses 

 of the epiglottis in deglutition, and the effects of its removal in the inferior animals. 

 The very elaborate memoir of Longet was published in the Archives Generates, 

 in 1841. Magendie showed that section of the inferior laryngeal nerves, para- 

 lyzing all the muscles of the larynx except the arytenoid and crico-thyroid, did 

 not interfere with deglutition, even in the case of liquids ; while after section of 

 the superior laryngeals, the deglutition of liquids was frequently followed by con- 

 vulsive cough. From this he concluded that the muscles animated by the supe- 

 rior laryngeal nerves were chiefly concerned in protecting the glottis. The later 

 and more minute experiments of Longet, however, proved this conclusion to be 

 an error. He showed that the cough occurred after the deglutition of liquids, 

 when the sensitive filaments of the superior laryngeals had been divided leaving 

 the muscular branches intact ; and he demonstrated that the difficulty lay in the 

 loss of sensibility of the mucous membrane, and not in paralysis of the crico- 

 thyroid muscles. 



