314 PHYSIOLOGY CHAP. 



ventricle, in such a way that the segments above and below were 

 united only by means of little muscular bridges and the rami of 

 the coronaries, synchronous contractions were found to persist 

 throughout the ventricular mass. These facts, which appeared 

 incompatible with nervous conduction, have, since Bethe's work 

 on the neuro-ganglionic system diffused throughout the frog's 

 myocardium, and that of Berkley on the mammalian myocardium, 

 lost all evidential value, since they can be explained by the 

 conduction of excitation through the fibrillary nervous network. 



Gaskell,.to exclude the intervention of nerves and ganglia 

 in the transmission of cardiac excitation, divided on the tortoise 

 the large nerve trunks that supply the ventricle, and on the frog 

 excised the interauricular septum with all its nerve trunks, and 

 found that the peristaltic propagation of beats from auricle to 

 ventricle was not interrupted. Analogous experiments with the 

 same results were carried out at a later time on the mammalian 

 heart by Krehl, in collaboration with Komberg. These experi- 

 ments, however, cannot be adduced in favour of the theory of 

 myogenic conduction, since it has been demonstrated by the 

 latest histological methods that the whole myocardium is pervaded 

 by minute ganglionic elements and nerve fibrils. 



Either on the hypothesis of myogenic, or on that of neurogenic 

 conduction, it is difficult to explain the fact of the brief arrests 

 or delayed transmission of the contraction wave at the points at 

 which it passes from one segment to the other of the heart, i.e. at 

 the junction between the sinus and the auricles, the auricles and 

 ventricle, the ventricle and the arterial bulb. 



It was formerly assumed, on the strength of the early 

 anatomical researches, that each of these parts of the heart 

 possessed a perfectly distinct system of muscle fibres. For the 

 heart of man and other mammals, in particular, Donders admitted 

 as a well-established fact that there was complete interruption 

 of the muscular walls corresponding with the auriculo- ventricular 

 groove, and he used this to account, on the neurogenic theory, for 

 the perfect a-synchronism between the systole of the auricles and 

 that of the ventricles. More recent and exact observations have 

 proved the existence of muscle bridges, which connect the different 

 parts of the heart, and form a united myocardium. 



As early as the end of 1876 Paladino, in the heart of man and 

 various other vertebrates, demonstrated the presence of muscular 

 fasciculi extending uninterruptedly from auricles to ventricles. In 

 1883, Gaskell demonstrated the same for the hearts of frog and 

 tortoise, and these observations were subsequently confirmed by 

 Stanley-Kent (1892-94), by His, jun., and by Engelmann, for the 

 heart of other vertebrates also. 



According to the recent and very minute researches of Tawara 

 (1905) on the human heart, this connecting system of auriculo- 



