THE HEART 61 



of tissue might be situated in any position. Histological investiga- 

 tion proves this free muscular continuity (Keith and Flack). With 

 regard to evidence of muscular conduction between auricle and 

 ventricle in the mammalian heart, it is usually held that the 

 A-V bundle effects this, and that the conduction by it is muscular. 

 The evidence that the A-V bundle is the sole passage of conduction 

 is also tolerably strong, although some investigators bring results 

 which appear to the contrary. The chief evidence in favour is 

 as follows : 



(1) Hering cut in the region of the A-V bundle in four dogs, 

 and in three cases out of four obtained allorhythmia. Tawara 

 showed by histological investigation that in three only was the 

 bundle cut ; the fourth had escaped. 



(2) Erlanger compressed the bundle in dogs by means of a 

 specially-devised atriotome, and succeeded in obtaining varying 

 degrees of arrhythmia and finally allorhythmia. Retzer confirmed 

 histologically the damage done to the bundle-. 



(3) Humblet has successfully obtained allorhythmia in dogs on 

 many occasions by ligaturing the A-V bundle. No allorhythmia 

 was produced when any other part of the septum was tied. 



(4) The evidence afforded by syphilitic disease of the bundle 

 in certain cases of Stokes-Adams disease. Several very satis- 

 factory cases with tracings and post-mortem examination of the 

 heart have been published. 



On the other hand, Kronecke.r states that in rabbits he is unable 

 to obtain any allorhythmia by ligature of the A-V bundle, and in 

 this he is confirmed by his pupil Imchanitsky. In some cases the 

 bundle was certainly not tied, but in others it is claimed to have 

 definitely been so. It may be that the heart of the rabbit affords 

 an exception, since Biggs also appears to have obtained uncertain 

 results upon the rabbit's heart. An interesting point, however, is 

 that Kronecker always attempted to tie the bundle through the 

 left auricle, and Humblet found in dogs that he was not successful 

 by this method. All the observers mentioned .above attack the 

 bundle through the right auricle. It is undoubtedly the more 

 certain method. There is great danger of getting above the 

 bundle or only obtaining part of it from the left side, owing to 

 the manner in which the left septal division comes off. 



The main evidence is undoubtedly in favour of the A-V bundle 

 being the sole path for the transmission of the impulse from auricle 



