THE CAUSATION OF THE HEART-BEAT 



1071 



sight evident in the adult heart. On superficial dissection the muscle 

 fibres both of auricles and ventricles are seen to arise from a fibro- 

 cartilaginous ring surrounding the auriculo-ventricular junctions, 

 leaving apparently no muscle continuous between the two cavities. 

 On this account it was thought for many years that the propagation 

 of the contraction from auricles to ventricles must occur by means of 

 nerve fibres. It was shown by Wooldridge and Tigerstedt that com- 

 plete destruction of functional continuity between auricles and 

 ventricles caused a failure of the sequence of contractions between 



FIG. 435. Left ventricle laid open to display the inter ventricular septum 

 on which the course of the auriculo-ventricular bundle and its ramifi- 

 cations are shown in black. (After TAWARA.) 



these two cavities, so that after the operation the auricles might be 

 beating at 80 per minute, while the ventricle rhythm was only 20 to 

 40 per minute. Bayliss and I found that in the normal mammalian 

 heart it was possible to reverse the normal sequence of rhythm by 

 artificially stimulating the ventricles at a rate greater than the normal 

 rhythm. It is difficult to conceive of any arrangement of neurons 

 which would propagate impulses impartially from auricles to ventricles 

 or from ventricles to auricles. Such a condition would seem to be in 

 contradiction lo the 'law of forward direction* which we;; find to 

 obtain throughout the nervous system. The difficulty of explaining 

 the phenomenon of reversed rhythm disappeared when it was shown 

 by Stanley Kent that there is actually a continuity of muscular 

 fibres between the auricles and ventricles. Kent's observations were 



