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PRINCIPLES OF GENERAL PHYSIOLOGY 







that Ernst Heinrich Weber made the announcement that he, with his brother 

 Eduard, had found this to take place. As Tigerstedt (1893) remarks, a new kind 

 of nervous action was brought to light, of which previously there had been 

 scarcely any idea, an action which could never have been discovered by anatomical 

 observations alone. A nerve, which supplied a muscle, was stimulated, and 

 instead of strengthening or accelerating the movements of the muscle, they 

 were slowed or stopped altogether. The original communication is, unfortunately, 

 published in an Italian medical journal difficult of access (Omodei's Annali di 

 Medicinal), But in 1846 Eduard Weber wrote an article, " Muskelbewegung," 

 for Wagner's " Handworterbuch der Physiologic," which included an account of 

 the work. It was found that stimulation of the vagus nerve inhibited the heart, 

 not only in the frog, but also in fish, birds, the cat, dog, and rabbit. It is well 

 to transcribe the words used : " Eine auf das Mannichfaltigste abgeanderte 



Reihe von Versuche, welche ich 

 gemeinschaftlich mit meinem 

 Bruder Ernst Heinrich aufgefiihrt 

 habe, hat uns zu der Entdeckung 

 geftihrt, dass durch Reizung 

 der Nervi vagi oder der Hirn- 

 theile, von dem sie entspringen, 

 das Tempo der rhythmischen 

 Bewegungen des Herzens ver- 

 langsamt und sogar das Herz ganz 

 zum Stillstand gebracht wird" 

 (P- 42). 



Since the work of the Webers, 

 a large number of investigators 

 have taken up the question of the 

 action of the vagus on the heart, 

 but we do not yet know what the 

 nature of inhibition is. The prob- 

 lem has been discussed in some 

 preceding pages of the present 

 work (pages 418-427). I wish here 

 to draw attention to some aspects 

 of it as affecting the heart, refer- 

 ring the reader especially to the 

 article by Gaskell (1900) for further 

 details up to the date of the 

 article. 





Fio. 232. ACTION OF VAGUS ON CONDUCTION FROM 

 AURICLE TO VENTRICLE. Dog's heart. 



Upper curve, beats of ventricle. 



Lower curve, beats of auricle. 



Upper signal, stimulation of vagus. 



Middle signal, artificial stimulation of auricle by single shocks, 



five per second. 

 Lower signal, time in seconds. 

 Before the stimulation of the vagus, the ventricle follows each 



auricular beat, with an occasional omission. 

 During stimulation of the vagus, it responds to each alternate 



beat onlv ; showing that the conducting power of the 



tissue is impaired. 



(Bayliss and Starling, 1892, 2.) 



As Engelmann pointed out 

 (1899), the action of the vagus is shown under four aspects : 



1. On the rate (" chronotropic "). This effect is shown in Figs. 113 (page 405) 



and 230 (page 681). 



2. On the strength of the beat (" inotropic "). Shown in the auricular 



tracing of Fig. 231. 



3. On the capacity of the muscle for conducting excitation (" dromotropic "). 



Shown for the turtle in Fig. 231, and for the dog in Fig. 232 

 (see the descriptions of the figs.). 



4. On the excitability to direct stimulation (" bathmotropic "). Mac William 



showed that the heart muscle, in some cases, is inexcitable under 



vagus stimulation (see page 407 above). 



How far these different effects are aspects of the same fundamental change is not 

 definitely known, but it seems probable. 



In the mammal, Cohn and Lewis (1913) have shown that the left vagus 

 has more effect on the junction between auricle and ventricle than the right 

 one has. On the other hand, the right nerve affects production of impulses in 

 the auricle more than the left one does. The facts are of interest in connection 

 with what we have seen as tothe facts of impulse formation in the sino-auricular 



