THE CIRCULATION OF THE BLOOD AND LYMPH 149 



tricular 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 

 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 

 assigning to the intrinsic cardiac nervous mechanism an im- 

 portant share in the 

 maintenance of the 

 rhythmical beat. If 

 this be the case, it 

 is natural to assume 

 that the extrinsic 

 nerves act on the 

 heart - muscle not 

 directly, but through 

 the ganglion - cells. 

 Some of these cells 

 lie on the course of 

 the vagus fibres, and 

 although the view 

 has been advocated 

 that they are simply 

 stations where the 

 inhibitory impulses 

 pass from medul- 

 lated to non-medul- 

 lated fibres, and 



FIG. 63. BLOOD-PRESSURE TRACINGS : RABBIT. 



Vagus stimulated at i. Stimulus stronger in B 

 Where possibly Other than in A (Hiirthle's spring manometer). 



anatomical changes 



and rearrangements occur, they may just as well be impor- 

 tant intermediate mechanisms which essentially modify the 

 physiological impulses falling into them and shape the visible 

 results that follow those impulses. The nervi accelerantes 

 are already non-medullated before they reach the heart, 

 and it is not known whether they make connection with in- 

 tracardiac ganglion-cells. The fact that the action of the 

 accelerantes can be restored by perfusing the heart with a 

 nutrient solution at a much longer interval after somatic death 

 than the action of the vagus strengthens the suggestion that 

 ganglion-cells are interposed on the inhibitory though not on 



