1893.] Nervous System on the Cardiac Rhythm, §c. 477 



ditions present, in this connexion, in two such animals as the hare 

 and the rabbit are very noteworthy. These animals, though very 

 closely allied, from a zoological point of view, live under very dif- 

 ferent functional conditions in certain respects : the rabbit is able to 

 run short distances with great rapidity, bat not to traverse long dis- 

 tances without intermission — this being no doubt in relation to the 

 fact of their having burrows to flee to ; the hare, on the other hand, 

 destitute of such means of protection, has to depend, in the open 

 country, upon its endurance in swift locomotion. On examining the 

 cardiac rhythm of this animal, I find it presents a remarkable con- 

 trast to that of the rabbit. In the latter animal, section of the vagi, 

 as is well known, causes comparatively little acceleration. In the 

 hare, on the other hand, in which the normal pulse-rate is much 

 slower (e.g., 64 per minute), the heart beats at an enormously in- 

 creased rate (e.g., 264 in the same animal) after the vagi have been 

 divided. 



In this animal, while the vagi are intact, the cardiac rhythm shows 

 very sudden and extensive changes when the animal is disturbed, &c. 

 These changes are probably due to alterations in the activity of the 

 vagus centre. 



Influence of Emotion upon the Cardiac Rhythm. 



The characteristic acceleration of the heart induced, by emotion in 

 animals and in man is probably due, largely or mainly, to a di- 

 minished activity of the cardio-inhibitory centre. The acceleration is 

 sometimes preceded by a phase of slowed action, due to excitation of 

 the same centre, and the entire effects present a very striking re- 

 semblance to those induced by afferent impulses. This correspondence 

 strongly suggests that the effects are, in the two cases, primarily de- 

 pendent on similar causes — changes in the activity of the vagus 

 centre — the primary slowing being due to a heightened activity of 

 the centre and the subsequent acceleration to a reaction in the way of 

 diminished activity — resembling what may be seen in certain other 

 centres under the influence of emotional conditions. The suddenness 

 and extent of the alterations in cardiac action sometimes induced 

 by powerful emotion are easily applicable in connexion with such a 

 view. 



Conclusion. 



From the evidence available on the subject, there is good reason 

 to believe that, in addition to the well-known influences of blood 

 pressure, asphyxial blood, &c, upon the vagus centre, the activity 

 of that centre is affected either in way of increase or diminution 

 by the play of afferent impulses from various parts, by impulses 



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