PAR VAGUM. 



above facts we believe that the oesophageal 

 filaments are chiefly incident and motor, and a 

 few of them only are sensiferous. 



Cardiac branches. We have in a former 

 part of this work (article HEART) had occasion 

 to state that several celebrated physiologists 

 have failed in exciting the muscular contractions 

 of the heart by irritation of the trunk of the 

 vagus before it gives oft' its cardiac branches, or 

 of these cardiac branches themselves. We have 

 very frequently repeated this experiment upon 

 animals immediately after death, and we have not 

 been able to satisfy ourselves that galvanic and 

 mechanical excitation of these nerves has any 

 effect in renewingor increasing the contractions of 

 the heart. No doubt we have not unfrequently 

 seen the contractions of the heart become more 

 frequent and vigorous during the performance 

 of this experiment ; but as similar changes in 

 the strength and rapidity of its contractions are 

 occasionally observed in an animal after death 

 when no artificial excitant has been applied to 

 these nerves, and from causes which cannot at 

 present be explained, we did not think ourselves 

 entitled to attribute these changes in the heart's 

 action to the excitation of the nerves. Valen- 

 tin* has stated that he has produced muscular 

 contractions in the heart in different animals by 

 irritation of the trunk of the vagus. He also 

 statesf that similar contractions of the heart 

 were produced by excitation of the spinal ac- 

 cessory and of the three superior (sometimes 

 also of the fourth) cervical nerves, and he main- 

 tains that the motor portion of the cardiac 

 nerves comes from the spinal accessory and the 

 superior cervical nerves. Longet]; mentions 

 that he failed in influencing the rhythm of the 

 heart by the application of galvanism to the 

 vagi in dogs, rabbits, and sheep, but very fre- 

 quently succeeded by scraping the cervical 

 cardiac branches of the vagus. Allowing that 

 it is possible to increase the contractions of the 

 heart by galvanic or mechanical excitation of 

 the vagus or its cardiac branches, it must be 

 admitted by every one that there is a very 

 marked difference between the heart and volun- 

 tary muscles in this respect, for all those who 

 have failed in their experiments on the nerves 

 of the heart, have felt not the smallest difficulty 

 in producing contractions of the voluntary 

 muscles by excitation of their nerves. The in- 

 creased frequency of the pulsations of the heart 

 observed during and for some minutes after the 

 division of the vagi may be fairly referred to 

 the struggles and terror of the animal, and the 

 feeble and rapid pulsation of the heart which 

 precedes death from this experiment is not 

 owing to any direct effect upon that organ. 

 The sudden death occasionally remarked after 

 the division of these nerves, and which some 

 of the early experimenters attributed to arrest- 

 ment of the contractility of the heart, was in 

 fact dependent upon the suffocation of the 

 animal by the suspension of the movements of 

 the muscles which dilate the superior aperture 



* Opus cit. p. 48, b'2 and 66. 



i Opus cit. p. 62. 



i Opus cit. &c. torn. ii. p. 314. 



of the larynx. We have related several expe- 

 riments which appear to prove that when in- 

 juries of the brain and mental emotions affect 

 the contractility of the heart, the nervous influ- 

 ence is not transmitted by the cardiac branches 

 of the vagi alone, but may also pass along 

 the filaments of the sympathetic or ganglionic 

 system of nerves. 



Pulmonary branches. Do the pulmonary 

 branches of the vagus contain motor filaments ? 

 We have made various unsuccessful attempts 

 to produce contractions in the muscular fibres 

 of the bronchial tubes by excitation of the vagi 

 in the neck.* Dr. C. T. B. Williams! was 

 also unsuccessful on attempting this experiment, 

 though he succeeded in producing contractions 

 in the bronchial muscular fibres by their direct 

 excitation, as by transmitting galvanism through 

 the substance of the lungs, &c. Longet and 

 Volkmann have not only succeeded in exciting 

 contractions of the muscular fibres of the 

 bronchii by direct stimulation, but also by ex- 

 citants applied to the branches of the vagus.J 

 To what extent are the pulmonary branches of 

 the vagus sensiferous ? Brachet relates some 

 experiments which seem to prove that the sen- 

 sation arising from the want of fresh air in the 

 lungs, or the besoin de respirer, is annihilated 

 by the division of vagi. Mr. Grainger|| re- 

 peated one of Brachet's experiments, and seemed 

 satisfied that his conclusions were correct. 

 There are certain sources of fallacy attending 

 the mode in which Brachet paformed his ex- 

 periments against which he has not taken the 

 necessary precautions. 



We have satisfied ourselves by numerous 

 experiments that the sense of anxiety arising 

 from the want of fresh air in the lungs conti- 

 nues after dividing the vagi when the access of 

 air to the lungs is prevented ;H and Volkmann** 

 and Longetft from their experiments have also 

 arrived at the same conclusion. It is possible 

 that certain impressions which may excite the 

 besoin de respirer are conveyed upwards to the 

 encephalon through the medium of the sympa- 

 thetic, but it is more probable that in the con- 

 ditions induced by the experiment it was more 

 immediately dependent upon the circulation of 

 ill-arterialized blood through the tissues of the 

 body, and more especially through the ence- 

 phalon. We do not mean to deny that im- 

 pressions conveyed along the vagi to the ence- 

 phalon may not excite the besoin de respirer ; on 

 the other hand, we believe that it is very prob- 

 able that this sensation as first felt, when the 

 respiration is suspended for a short time in the 

 healthy condition of the body, is dependent upon 

 impressions conveyed along this nerve. When, 



* Opus cit. for 1839. 



t Transactions of British Scientific Association 

 for 1840, p. 411. 



f Longet, opus cit. torn. ii. p. 289, and Volk- 

 mann in Wagner's Handworterbnch der Physio- 

 logie, article Nervenphysiologie, p. 586. 



Systeme Nerveux Ganglionaire, p. 133-4-5. 



|) On the Spinal Chord. 



f Opus cit. for 1838. 



** Muller's Archives for 1841. See also Forbes' 

 British and Foreign Review for Jan. 1842, p. 223. 



tt Opus cit. torn, ii., 291-2, 1842. 



