THE NERVOUS REGULATION OF THE HEART 



1*3 



all diminished, even when the auricle is beating very feebly during 

 inhibition. When the auricle is completely stopped, which does 

 not occur so readily as in the frog, the ventricle also stops for a 

 short time, but soon begins to beat again with an independent 

 rhythm of its own. In the frog the ventricle is directly affected 

 by stimulation of the vagus, and the force of its beats is diminished 

 independently of the inhibitory effect^ in the auricles (Practical 

 Exercises, pp. 196, 201). 



The inhibitory fibres, then, influence the heart particularly 

 through the auricles ; they are par excellence auricular nerves. On 

 the other hand, the accelerantes in all mammals which have been 

 investigated not only extend to the ventricles, but are even mainly 

 distributed to them. 

 They are emphatically 

 ventricular fibres, and 

 in accordance with its 

 greater mass the left 

 ventricle receives more 

 fibres than the right. 



Stimulation of the 

 accelerator nerves in 

 the dog causes an in- 

 crease in the force of 

 both the auricular and 

 ventricular contraction, 

 and as a rule, in addi- 

 tion, some increase in 

 the rate of the beat. 



As to the nature of 

 the physiological link- 

 age between the cardiac 

 nerves and the mus- 

 cular tissue of the heart 

 we know but little. 

 Ganglion-cells lie on the course of the vagus fibres after they have 

 entered the heart, and although the view has been advocated that 

 they are simply stations where the inhibitory impulses pass from 

 medullated to non-medullated fibres, and where possibly other 

 anatomical changes and rearrangements occur, they may be inter- 

 mediate mechanisms which essentially modify the physiological 

 impulses falling into them. It has been stated that in the dog the 

 right vagus controls chiefly the rate of the heart, and the left vagus 

 chiefly the conduction from auricles to ventricles, and the suggestion 

 has been made that this is because the right vagus has a special 

 relation to the sino-auricular node, in which impulses are supposed 

 to arise, and the left vagus a special relation to the auriculo-ven- 



ig. 75. Blood-Pressure Tracings: Rabbit. Vagus 

 stimulated at i. Stimulus stronger in B than in 

 A (Hurthle's spring manometer). 



