310 



OF THE CIRCULATION OF THE BLOOD. 



surface in the neck, by means of an interrupted current of electricity caused 

 the rhythmical movements of the heart to become slower, and if the current 

 were sufficiently strong arrested its movements altogether. Now in the case 

 of any voluntary muscle the passage of such a current through the nerves 

 supplying it produces either simple contraction, or if the shocks be suffi- 

 ciently frequent, tetanus, but in the case of the heart the effect produced is, 



FIG. 127. 



(an-tio-inJrlb J&jrc 



' fibres\ . " V 



Jftrru> fj> 



IfnliiMc* 



Vftgo not/)'' 



Aorta. 



firstdors: 



. 

 ~Sntn.Syi.nfi 



accei.tocri&js 



Aorta 



Diagram to aid in understanding the action of the nerves upon the Heart. The Right half repre- 

 sents the course of the inhibitory, and the Left the course of the accelerating nerves of the Heart ; the 

 arrows showing the direction in which impressions are conveyed. The ellipse at the upper extremity 

 of the Vagus looking like the section of the nerve is intended to represent the Vagal nucleus or centre. 



on the contrary, that of complete relaxation. The cessation of the rhythmi- 

 cal action in diastole is not, however, of long duration ; contraction soon 

 recommences, notwithstanding the continued application of the electrical 

 stimulus, though it can be again arrested by passing the interrupted current 

 through a fresh portion of the nerve situated lower down or nearer the heart. 

 Dr. Rutherford has shown that the induced current obtained from Du Bois- 

 Reymond's induction machine and a single Daniell's cell begins to slow the 

 heart in the frog when the primary and secondary coils are distant about 

 200-300 millimetres, and that arrest of the heart's action occurs when the 

 distance is about 100 millimetres. Comparative trials showed that a very 

 much stronger irritant is necessary so to stimulate the Cardio-inhibitory 



