THEORIES OF THE HEART-BEAT 



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from the ventricle with the same result. If the heart be divided lengthwise, 

 its parts will continue to pulsate rhythmically. The ventricle remains 

 comparatively quiet, contractions occurring at longer intervals, if at all. 

 However, the isolated ventricle remains irritable so long as bathed in 

 blood or in a balanced Ringer solution, and will contract upon receiving 

 a slight stimulus. In fact, a single stimulus will often call forth a series of 

 contractions of the ventricle. The frog's ventricle, when its muscular 



FIG. 175. Isolated Nerve Cells from the Frog's Heart. 7, Usual form; II, twin cell; C t 

 capsule; A 7 ", nucleus; P, process. (From Ecker.) 



and nervous connections with the auricle are physiologically severed, as 

 by crushing, will remain quiet when fed by its own blood, though it will 

 contract rhythmically when fed with physiological salt solution. 



It is thus seen that the rhythmical movements of these parts of the 

 heart appear to be more marked in the parts at the venous end of the 

 organ, i.e., the sinus and auricle, and less marked in the ventricular end. 

 Ventricular pieces contract when still connected with the auricles but do 

 not readily contract in the ordinary condition even when irrigated with 

 blood. These are regarded as facts peculiarly in favor of the view that 

 the rhythm is inherent in the special nervous elements of the heart. 



This view which has long been known as the neurogenic theory, attri- 

 butes the remarkable power of the heart to continue contractions after 

 removal from the body, and presumably while in the body, to the presence 

 of the collections of nerve cells within the walls of the heart itself. The 

 local nervous mechanism in the frog consists of three chief groups of cells 

 or ganglia. The first group is situated in the wall of the sinus venosus at 

 the junction of the sinus with the right auricle, Remak's ganglion. The 

 second group is placed near the junction between the auricles and ven- 

 tricles, Bidder's ganglion. The third is in the septum between the auricles, 

 wn Bezold's ganglion. Small ganglia have been described for the base of 

 the ventricle, but no ganglia are present in the apical part of the ventricles, 

 though isolated neurones have been found. The nerve cells of which 

 these ganglia are composed are generally unipolar, seldom bipolar. Some- 



