PAR VAGUM. 



897 



however, the respiration has been suspended 

 for a longer time and venous blood begins to 

 circulate along the arteries, the other excitants 

 of the beiwin de respirer come into operation. 



Brachet,* Krimer,f and Longet,J have from 

 their experiments arrived at the conclusion that 

 the sensations occasioned by irritation of the 

 inner surface of the trachea and bronchial tubes, 

 and which usually precede coughing, are anni- 

 hilated by dividing the vagi. We have made 

 repeated experiments on this point, and though 

 we could not satisfy ourselves that these sensa- 

 tions were affected to the extent maintained by 

 these authors, we believe that they are at least 

 blunted. 



To what extent do the filaments of the vagi 

 act as incident nerves? It has been 'proved by 

 the experiments of Legallois, Flourens,|| and 

 others, that all the respiratory and muscular 

 movements cease on destroying the medulla 

 oblongata, though the other parts of the ence- 

 phalon situated above this may be injured in 

 various ways without necessarily producing 

 this effect. It is further well known that if the 

 spinal chord be cut across, all the respiratory 

 muscles are paralysed which receive their 

 nerves from that portion of it below the point 

 where it was divided, while those muscles 

 which receive their nerves from that portion of 

 the spinal chord still continuous with the me- 

 dulla oblongata perform their usual functions. 

 From these and other facts it may be consi- 

 dered as ascertained that all impressions made 

 at the lungs and elsewhere capable of causing 

 respiratory movements, must be conveyed to 

 the medulla oblongata before they can produce 

 any reflex excitation of the muscles of respira- 

 tion. That the vagi can convey these impres- 

 sions from the lungs is not only rendered pro- 

 bable from their attachment to the medulla 

 .oblongata, but may almost be considered as 

 proved by the result of the experiments upon 

 the spinal chord to which we have just referred. 

 It, however, by no means follows that the vagi 

 are the sole excitant nerves of respiration. It 

 has been fully ascertained by numerous expe- 

 rimenters, more especially by those who have 

 investigated the functions of this nerve from the 

 time of Legallois, that an animal will continue 

 to breathe after the division of both vagi in the 

 neck, if care be taken to secure the ingress and 

 egress of air to and from the lungs. It is now 

 well known, as we have already had occasion 

 to point out in examining the functions of the 

 laryngeal branches, that if the vagi be injured 

 above the origin of the recurrent laryngeals, 

 none of the muscles attached to the arytenoid 

 cartilages can any longer act in unison with the 

 muscles of respiration, all their movements 

 cease, and the superior aperture of the larynx 

 can no longer be dilated during inspiration. 

 If the larynx be large, and the animal refrain 



* Oper. cit. p. 157-8-9. 



t Untersuchungen liber den Husten, as quoted bv 

 Mliller. 



t Oper. cit. torn. ii. p. 289. 



Sur le Principe de la Vie. 



|| Recherches Experimentales stir les Propriotes 

 et les Fonctions du Systeme N'erveux. &c. Paris, 

 1824. 



VOL. III. 



from any violent effort, an adequate quantity of 

 air may still find its way to the lungs, and the 

 respirations are at first performed with ease. 

 If, on the other hand, the larynx be small, its 

 superior aperture may be mechanically closed 

 and the animal may be immediately suffocated, 

 or the air may still pass through the larynx but 

 in diminished quantity, and the animal may 

 labour under dypsnca from the moment the 

 nerves are divided, up to its death. Even when 

 means are taken to secure the free entrance of 

 air into the lungs, an immediate and marked 

 diminution in the frequency of the respiratory 

 movements follows the division of both vagi 

 in the neck. A. G. F. Emmert concluded, but 

 apparently more upon theoretical grounds than 

 from any direct observations made in the two 

 experiments he had at that time performed on 

 rabbits, that after lesion of the vagi the respira- 

 tions become less frequent and prolonged.* 

 Mayer reckoned the number of respirations, 

 both before and at various periods after section 

 of these nerves in five experiments upon the 

 ass, dog, and rabbit, and found a very marked 

 diminution in their frequency after dividing the 

 nerves.f Mr. Broughton mentions, that in a 

 horse in which the vagi were divided " the 

 respirations became slow, twelve in a minute ;" 

 and in another horse " the respirations fell to 

 five in the minute. "J At what period after 

 the division of the nerves these last observations 

 were made, and what was the number of the 

 respirations previous to the commencement of 

 the experiments, we are not informed. Sir 

 Astley Cooper has given the result of two expe- 

 riments upon rabbits which well illustrate the 

 effect of the division of the vagi upon the respi- 

 ratory movements. In our experiments we 

 ascertained that the diminution in the frequency 

 of the respiratory movements, generally to less 

 than half of their former number, is an imme- 

 diate effect of thedivision of both vai. The respi- 

 ratory movements seem to be performed more 

 slowly, and, generally, even from the first, in a 

 somewhatheavmgmanner.il Arnold in his expe- 

 riments upon hens also observed a very consi- 

 derable diminution in the frequency of the re- 

 spiratory movements.^ Brachet has asserted** 

 that an animal continues to breathe after sec- 

 tion of the vagi, because it has acquired the 

 habit of using the respiratory muscles. Dr. 

 Marshall Hall has maintained that after the 

 vagi are divided the respiratory movements are 

 no longer a function of the excito-motory but 

 of the cerebral portion of the nervous system ;f-f 



* Archiv. fur Physiologic von Reil und Auten- 

 rieth, Neunter Band. 1809, s. 417. 



t Tiedemann's Zeitschrift fur Physiologic, 

 Zweiter Band, 1826, s. 77. 



| Quarterly Journal of Literature, Science, &c. 

 vol. x., p. 305 and 307. 



Guy's Hospital Reports, No. 3, Sept. 1836, 

 p. 409. 



|| Transactions of British Scientific Association 

 for 1838, and Edin. Med. and Surgical Journal tor 

 1839, vol 51. 



IT Bemerkungen u'ber den Bau d^s Hirns und 

 Riickenmarks, &c. s. 148. Zurich, 1838. 



** Oper. cit. p. 132. 



tt Philosophical Magazine for Jan. 1835. Lec 



3 M 



