566 



Mr. T. Lewis. 



tissue, though nerves pass freely over the auriculo-ventricular groove. 

 The musculatures of the two chambers were, in fact, widely believed to be 

 disunited. It seemed as if either Gaskell's conclusions for the cold-blooded 

 heart lacked finality, or that a fundamental difference exists between the 

 mechanism in frog and mammal. The obvious discrepancy was removed 

 from the minds of English physiologists by Kent's description of a muscle 

 union between the two chambers in the mammal in 1892 (13). A year later, 

 His described the muscle bridge more distinctly, and made the first experi- 

 ments upon it (11). The final experiments were made by the Americans, 

 Erlanger (5) and Cohn(3), and others (10). It has been proved beyond all 

 reasonable doubt that this muscle bridge, which runs from the auricular 

 to the ventricular septum, is in the mammalian heart the sole path by 

 which impulses are conveyed from auricle to ventricle. That pressure 

 upon or cooling of this bundle hinders the passage of the impulse, that 

 division of this bundle completely dissociates the movements of auricle 

 and ventricle, is now recognised ; these effects are regularly obtained in a 

 number of experimental laboratories. 



Distribution of the Wave in the Ventricle. 



I pass over the earliest experiments upon the spread of the contraction 

 wave through the ventricle. The observations were electrical, and were 

 inaugurated by Burdon Sanderson ; they were contradictory because the 

 complexity of the spread was not appreciated. 



In respect of the spread in the mammalian ventricle a great step in the 

 progress of knowledge came with the anatomical discovery of Tawara (22), 

 the Japanese. Many years before Purkinje had described a network of 

 highly differentiated cells lying beneath the endocardium in mammals. 

 The functions of these cells were in his time quite unknown. Tawara 

 demonstrated that they compose in each ventricle a striking basketwork, 

 lining each chamber. He traced the ending of the muscular bundle which 

 unites auricle and ventricle into a right and a left division, each of which 

 by a few chief strands unites with the basketwork lining the corresponding 

 ventricle. He concluded, and rightly concluded as it transpires, that the 

 bundle forms with its branches and arborisations the channels by which 

 the impulse to the mammalian ventricle is distributed. The experimental 

 proof that this is so is now forthcoming. 



The ventricle is the chamber which accomplishes the heart's real work ; 

 it is powerful muscle, arranged around the blood-containing cavities, and 

 forming to these cavities a thick wall. The muscle fibres are arranged in 

 an intricate fashion, largely in the form of broad spiral bands, some of 



