140 



A MANUAL OF PHYSIOLOGY 



only because in the normally beating heart the ventricle 

 takes the time from the auricle. The strength of the ven- 

 tricular contractions is not at 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 

 effects in the 

 auricles (Practical 

 Exercises, pp. 178, 



Stimulation of 

 the accelerator 

 nerves in the dog 

 causes an increase 

 in the force of both 

 the auricular and 

 ventricular con- 

 traction, and, as a 

 rule, in addition, 

 some increase in 

 the rate of the 

 beat. 



As to the nature 



of the physiological linkage between the cardiac nerves and the 

 muscular tissue of the heart we know but little. It has 

 been supposed that within the heart itself there may exist 

 peripheral nervous mechanisms which mediate between the 

 nerves and the muscle. We have already given reasons 

 for denying to the ganglion cells any important share in 

 the maintenance of the rhythmical beat, but we have not 

 assigned them any function. It has been suggested that 

 the ganglia may act as local inhibitory, or even as local 

 augmentor, centres. Others, however, have inclined to the 



FIG. 51. BLOOD-PRESSURE TRACING (RABBIT). 



Vagus stimulated at i. Stimulus stronger in B than 

 in A (Hiirthle's spring manometer). 



