THE CIRCULATION OF THE BLOOD AND LYMPH 129 



which pass down the anterior and posterior borders of the septum 

 to end in two clumps of nerve-cells (Bidder's ganglia), situated at 

 the auriculo-ventricular groove. These ganglia in turn give off 

 fine nerve-bundles to the ventricle, which form three plexuses, one 

 under the pericardium, another under the endocardium, and a third 

 in the muscular wall itself, or myocardium. From the last of these 

 plexuses numerous non-medullated fibres run in among the muscular 

 fibres and end in close relation with them. Similar plexuses of nerve- 

 fibres exist in the mammalian ventricle. But while a few scattered 

 ganglion cells are found in the upper part of the ventricular wall, 

 neither in the mammal nor in the frog have any been as yet demon- 

 strated in the apical half. In the rat's heart, according to the careful 

 recent observations of Schwartz, true ganglion cells a.re confined to 

 an area on the posterior surface of the auricles. 



Cause of the Rhythmical Beat of the Heart. It was long sup- 

 posed that the presence of ganglion cells was the clue to the 

 explanation of the automatic contraction of the heart, and 

 by some they are still looked upon as centres from which 

 impulses are sent out at regular intervals to the cardiac 

 muscular fibres. Nor on a superficial view are arguments 

 wanting in support of this opinion. We divide, in the frog, 

 the sinus which contains ganglion cells from the lower 

 portion of the heart, and it continues to pulsate. We cut 

 off the apex, which contains no ganglion cells and it remains 

 obstinately at rest. Further, if, without actually cutting off 

 the apex, we dissever it physiologically from the heart by 

 crushing a narrow zone of tissue midway between it and the 

 auriculo-ventricular groove, we appear to abolish for ever its 

 power of rhythmical contraction. The frog may live for 

 many weeks, but in general the apex remains in permanent 

 diastole. It can be caused to contract by an artificial 

 stimulus, but it neither takes part in the spontaneous con- 

 traction of the rest of the heart, nor does it start an in- 

 dependent beat of its own. What can be simpler than to 

 suppose that the sinus beats because it has ganglion cells in 

 its walls, and that the apex refuses to beat because it has 

 none ? But if we pursue our investigations a little farther, 

 we shall find that the matter is more complex. Let us 

 inquire, for instance, what happens to the auricles and 

 ventricle of the frog's heart when the sinus is cut off. The 

 answer is that, as a rule, while the sinus goes on beating, 

 the rest of the heart comes to a standstill, in spite of the 



9 



