N euro -Muscular Structures in the Heart. 



199 



In other words, it appears that the aurieulo-ventricular bundle is not the 

 only path by which the functional connection between the auricle and 

 ventricle may be established, and that " the co-operation between the auricle 

 and ventricle is not necessarily dissolved because the aurieulo-ventricular 

 bundle has been put out of action " (4). 



The experimental evidence to which reference has been made is at present 

 unpublished, and was first brought to my notice by Prof. Leonard Hill, to 

 whom I am indebted for permission to refer to it. I have recently repeated 

 the experiments, and can have no doubt as to their real significance. 



The evidence is of the following character : — 



If in the beating heart of a mammal the anatomical connections between 

 the left auricle and left ventricle are severed, and the section is carried 

 through the septum also, thus leaving only the right ventricular wall attached 

 to the auricle, even under these circumstances co-ordinated beats pass over 

 the aurieulo-ventricular junction, the ventricular contraction following the 

 auricular in its proper sequence. 



With such clinical and experimental evidence before us it is idle to assert 

 that no conducting path exists other than the well-known and well-defined 

 aurieulo-ventricular bundle, and the question is no longer " Does a connec- 

 tion exist ? " but " What is the nature of the connection ? " 



It may perhaps be recollected that as long ago as 1892 (5, 6) I described 

 the existence of a connection in this situation, viz., between the outer wall 

 of auricle and ventricle. The importance of the recently-described septal 

 connections overshadowed this other observation, however, and its significance 

 was not appreciated. It was only when the fact that the aurieulo- 

 ventricular bundle could be destroyed without abolishing the co-ordinated 

 action between the chambers that the importance of additional conducting 

 paths was brought into prominence. 



During the past few years my work on the human heart has shown that 

 there exists a mechanism which may perhaps help to elucidate the manner 

 in which these hitherto imperfectly explained transferences of activity are 

 brought about, and although the details have not all been worked out, it may 

 perhaps be of use to place the facts on record. 



It is well known that in a series of sections made through the aurieulo- 

 ventricular junction an outstanding feature is the large number of nervous 

 structures present. It is no uncommon thing to find from 20 to 30 nerve 

 trunks cut across, some 50 fi to 100 /x in diameter, most of them lying in the 

 fat and connective tissue of the groove, whilst in addition to these there are 

 trunks of large size lying amongst the muscular tissue, and apparently 

 derived directly from those in the groove. 



