THE RHYTHMIC AND PERISTALTIC MOVEMENTS 105 



kind of muscle fibre known as Purkinje's fibres. He described 

 how these peculiar large fibres passed into the ordinary 

 muscle fibres of the ventricle on the one side, and formed a 

 tangled knot of peculiar small fibres on the auricular side, the 

 contingents of which passed into separate auricular muscles. 

 This knot is known by the name of the auriculo-ventricular node. 



A similar structure has been described at the junction of the 

 veins and the auricles, " the sino-auricular node " of Keith and 

 Flack, from which the beats of the heart start. This sino- 

 auricular node has been further investigated by Lewis ; it is a 

 structure of the same kind as the auriculo-ventricular node, and 

 forms an elongated mass in the sulcus terminalis at the junction 

 of the right auricle and vena cava superior. Here the reticulated 

 muscle strands of the auricles come together to form a muscular 

 band known as the taenia terminalis, from which muscle fibres 

 pass into the vena cava superior and inferior. The peculiar fibres 

 which form the sino-auricular node are of the same kind as those 

 in the auriculo-ventricular node, "being small, about a half or 

 third the breadth of those of auricular fibres proper" (Lewis, p. 2). 



The theory that I put forward to explain the peculiarities of 

 the heart beat in the cold-blooded vertebrates, has thus received 

 striking confirmation in the investigations on the heart of 

 warm-blooded animals, and has been confirmed by recent investi- 

 gation on cold-blooded animals ; in all cases the parts of the heart, 

 where rhythmic beats may start, and where the conduction of 

 a contraction wave is slower, consist of muscular tissue of a more 

 primitive type, the remains of the canalis auricularis and of the 

 sinus venosus. 



This then represents what has been called the myogenic 

 theory of the heart beat, in which the initiation of a rhythmic 

 beat and of the maintenance of a due sequence of contraction 

 from cavity to cavity are ascribed to the muscular rather 

 than to the nervous elements in the heart. At the same 

 time this theory does not imply, and has never been intended by 

 me to imply, that the nervous tissues in the heart have nothing 

 to do with the heart beat. I have always been a strong 

 believer in the close connexion between the muscle-cell and 

 its nerve and nerve-cell, and consider that there is abundant 

 evidence to show that the well-being of the muscle is dependent 

 upon the integrity of its connexion with its nerve-cell ; with the 



