222 NEKVOTTS SYSTEM. 



not close when irritated. If the inferior laryngeals be then 

 divided, the glottis is mechanically closed with the inspira- 

 tory act, and the animals often die of suffocation. When we 

 sCall to mind the varied sources from which the pneumogas- 

 trics receive their motor filaments, it is easy to understand 

 how certain of these may preside over the vocal movements, 

 and others, from a different source, may animate the respira- 

 tory movements. 



As we should naturally expect from what has already 

 been said, section of the inferior laryngeal nerves paralyzes 

 both the vocal and the respiratory movements of the larynx. 

 It is not necessary to refer in detail to the ancient and mod- 

 ern experiments illustrating this point, the former dating 

 from the time of Galen. In adult animals, the cartilages of 

 the larynx are sufficiently rigid to allow of inspiration after 

 the organ has been completely paralyzed ; but in young ani- 

 mals, the glottis is closed, and suffocation ensues. "We have 

 generally observed in cats, that suffocation follows immedi- 

 ately upon section of the recurrents or of the pneumogastrics 

 in the neck. 



The impediment to the entrance of air into the lungs is 

 a sufficient explanation of the increase in the number of the 

 respiratory acts after division of both recurrents. It has 

 been observed by Longet, that the acceleration of respiration 

 is much greater in young than in adult animals. This does 

 not apply to very young animals, in which section of the re- 

 currents produces almost instant death. 1 



Waller and Prevost have shown that feeble galvanization 

 of the central ends of the inferior laryngeals, after their di- 

 vision, produces rhythmical movements of deglutition, gen- 

 erally coincident with arrest of the action of the diaphragm. 

 These phenomena are generally observed in rabbits, but 

 they are not constant. 3 The reflex action of these nerves in 



1 LONGET, Tralte de physiologic, Paris, 1869, tome iii., p. 533. 



2 WALLER ET PREVOST, Phenomenes reflexes de la deglutition. Archives de 

 physiologic, Paris, 1870, tome iii., p. 346. 



