110 DR RUTHERFORD ON THE INFLUENCE OF THE VAGUS 



Function of the Inferior Cardiac Branch of the Vagus. Is it motor as 



well as inhibitory ? 



Effect of Stimulating the Nerve. 



In 1845, the brothers Weber* made the well-known observation that, on 

 irritating the vagi, or those portions of the central nervous system from which 

 they spring, that the heart beats more slowly, and may even come to a stand- 

 still in a state of relaxation. From this observation they concluded that the 

 vagus exercises an inhibitory power over the heart's action. The accuracy of 

 the experiment has ever been beyond dispute, but the explanation, though now 

 accepted by nearly all — if not by all — physiologists, has nevertheless been 

 opposed by such distinguished investigators as ScHiFF,t Moleschott,;}; and 

 Lister. §. These authorities, while admitting that powerful stimulation of the 

 vagus arrests cardiac action, maintained that gentle stimulation quickens it. 

 They, therefore, concluded that the vagus is really a motor nerve of the heart, 

 and that the arrest of cardiac action which follows powerful irritation of the 

 nerve, is due to exhaustion of the latter. 



As it is unnecessary to slay the slain, I need not adduce the arguments 

 necessary to show how fallacious is the method of reasoning upon which these 

 authors have hinged their conclusion, — that has already been ably done by 

 Pfluger,|| Von Bezold,H and others. I will only make a single remark, 

 namely this, — were it true that while powerful stimulation slows the heart, 

 weak stimulation quickens it, the conclusion that both effects must necessarily 

 be due to the influence of the stimulant upon the same fibres of the vagus is by 

 no means warranted. It seems to me that the only legitimate explanation 

 which Schiff and others could have given of their facts, is that the excitement 

 of the heart due to stimulation of the lower end of the vagus — after its section 

 in the neck — results either from general excitement of the animal, or from the 

 presence of cardiac motor nerves in the vagus-^z^ addition to those which 

 inhibit the heart's movements ; a weaker stimulus being necessary for the 

 former than is required for the latter. 



It is settled beyond all dispute that the inferior cardiac branch of the vagus 

 contains fibres which inhibit the heart. The experiments hitherto performed 



* Omodei Annali Universali di Medicina, vol. cxvi. p. 225, November 1845. 

 "J* Experimentelle Untersucbungen uber die Nerven des Herzens. Arcbiv. fiir Pbysiolog. Heil- 

 kunde 8 ter Jabrgang. 



% Wiener Med. Wocb.enscb.rift, 25ter Mai 1861. 

 § Proc. Roy. Soc. vol. ix. p. 367. 



|| Reichert's and Du Bois Retmond's Arcbivs, 1859, p. 13. 

 IT Lib. cit. Erste Abtbeilung. 



