THE CIRCULATION OF THE BLOOD AND LYMPH 131 



affect the co-ordination. It is not permissible to transfer these 

 results wholesale to higher hearts, and especially the conclusions 

 as to rhythm, conduction, and co-ordination. But in the case 

 of the higher animals also facts may be adduced in favour of the 

 neurogenic origin of the beat. The isolated auricular appendices 

 of the mammalian heart, in which no ganglion-cells have been 

 found, refuse to beat spontaneously. If in the frog we divide 

 the sinus, which is conspicuously rich in ganglion-cells, from the 

 lower portion of the heart, it continues to pulsate. A fragment 

 from the base of the ventricle will go on contracting if it includes 

 Bidder's ganglion, but not otherwise. We cut off the lower 

 two-thirds of the frog's ventricle, the so-called apex preparation, 

 which either contains no ganglion-cells or is relatively poor in 

 them, 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 



FIG. 53. THE HEART AND THE HEART NERVES OF LIMULUS : DORSAL VIEW 



(CARLSON). 



(The heart is figured one-half the natural size of a large specimen.) 



aa, Anterior artery ; la, lateral arteries ; In, lateral nerves ; mnc, median nerve- 

 cord ; os, ostia. 



between it and the auriculo-ventricular groove, we abolish for 

 ever its power of spontaneous 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 contraction 

 of the rest of the heart, nor does it start an independent beat of 

 its own. 



What can be simpler than to assume that the sinus beats 

 because it has numerous ganglion-cells in its walls, and that 

 the apex refuses to beat because it has comparatively few or 

 none ? Could we pick out the nerve-cells from the sinus, without 

 injuring the muscular tissue, as easily as we can extirpate the 

 median nerve-cord in Limulus we may well suppose that it would 

 lose its power of automatic contraction. And although, if we 

 pursue our investigations a little farther, facts may emerge which 

 seem to contradict the neurogenic hypothesis, the contradiction 

 is usually only apparent. Let us inquire, for instance, what 



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