228 REPORTS ON THE STATE OF SCIENCE. — 1915. 



pass over the auriculo-ventricular groove to the ventricle as soon as 

 a physiological section has been made through the septal connection 

 (auriculo-ventricular bundle). I have found it to be the case, however, 

 that the pulsations continue to be transmitted to the ventricle, in spite 

 of the severance both of the septal connection and of the greater portion 

 of the outer walls of the chambers, in those cases where the part 

 remaining unsevered includes the particular tract of the heart already- 

 referred to as showing histologically the presence of the right lateral 

 connection. Indeed, it has been possible to reduce this tract to very 

 narrow limits, and I have found the following experiment to be uni- 

 formly successful, provided the part remaining is situated at the exact 

 spot described. 



An animal having been anassthetised and the thorax opened, a thin 

 sharp pointed knife is passed through the heart at the level of the 

 auriculo-ventricular junction, about half an inch from the right side, 

 the edge of the knife being towards the left. The knife is at once carried 

 across the heart towards the left, severing in its course the major part 

 of the junctional tissues between the right auricle and the right ventricle, 

 the septal connections, including the auriculo-ventricular bundle, and 

 the whole of the connections between the left auricle and the left 

 ventricle. Tn such circumstances the heart still continues to beat, 

 and the two sets of chambers, the auricles and ventricles, maintain 

 their co-ordination. 



By careful dissection it is possible to reduce the width of the 

 bridge of tissue connecting the auricles and ventricles until it is no 

 more than a couple of millimetres across, without in any way inter- 

 fering with the co-ordinated action of the two sets of chambers. 



Sections made subsequently have shown that muscular fibres are 

 present throughout the entire length of this bridge, and that they form 

 a continuous tract of conducting tissue, connected above with the 

 auricle and below with the ventricle. 



Any considerable narrowing of the bridge beyond this point — or a 

 complete rupture of it — results in a cessation of the co-ordinated action, 

 and a like result is obtained unless the situation of the bridge is very 

 carefully selected. If, after a narrowing of the bridge to about two 

 millimetres, the heart is allowed to remain until the automatic beats 

 originating in the auricle cease and all the chambers are quiescent, it is 

 still possible to excite beats artificially in either auricle or ventricle by 

 appropriate stimuli, and it is found under these conditions that contrac- 

 tions excited in the auricle pass through to the ventricle, whilst beats 

 excited artificially in the ventricle pass through to the auricle and give 

 rise to auricular contractions. 



The conclusions which may be drawn from the facts stated appear 

 to be as follows: — The widely accepted statement that the auriculo- 

 ventricular bundle constitutes the only path of conduction between 

 the auricle and ventricle can no longer be upheld. Both histological 

 and experimental evidence go to prove that an alternative path exists 

 in the situation described. 



This alternative path can function and can preserve co-ordination 

 between the auricles and ventricles aft^r the septal connections (auri- 



