Upon the Motion of the Mammalian Heart. 561 



discovered in the auricular wall of the amphibious heart ; the functions of 

 these cells were not understood, they were for many years wrongly interpreted. 

 The incorrect interpretation obtained a powerful hold upon men's minds, 

 colouring their thoughts and their observations. The cells were regarded as 

 central regulating stations, from which the rhythm of the heart was 

 propagated, from which the sequence of chamber contraction was ordered. 

 It is to this period that the observations of Stannius belong. Though 

 doubts arose at a later date, it was not until W. H. G-askell published his 

 observations (9), that the hypothesis of a neurogenic control of sequence in 

 the sense in which it was then employed was laid finally to rest. The 

 discovery of Gaskell which now concerns us followed and was prompted by 

 the work of that distinguished English scientist Eomanes, upon the contractile 

 bell of jelly fishes. Eomanes (20) proved that the contraction is propagated 

 as a wave through the bell and that the direction of its spread is governed by 

 continuity of the tissue. The wave of contraction could be diverted by 

 systematic incisions, zig-zag or spiral as the case might be, and would follow 

 regularly the path devised for it, however unusual such a path. Gaskell 

 demonstrated the same fact in the muscular wall of the auricle, proving 

 beyond cavil that contraction travels as a wave, and that tire contraction of 

 one segment of an isolated strip is provoked by the passage of the contraction 

 wave into it from a neighbouring segment. He showed, as Eomanes had done 

 for the umbrella of Medusa, that the sequence of contraction in the elements 

 of a strip of heart muscle is independent of the natural order in which these 

 elements contract, that continuity alone guides the flow of the wave. He 

 showed that the muscle of the heart may be so cut as to disorganise the 

 supposed system of governing nerve fibres united to a central nerve station 

 without interrupting the passage of the wave. He clearly enunciated his 

 conclusion that the passage of a contraction wave from one mass of heart 

 muscle to another depends upon the bridging of the gap between them by 

 muscle tissue and upon the functional integrity of the bridge. He demon- 

 strated that when one mass of heart muscle contracts in sequence to another, 

 the stimulus which promotes the contraction of the former is derived from the 

 activity displayed by the latter. If the functional integrity of 'the bridge is 

 impaired by such an experimental procedure as pressure upon it, then the 

 response in the distal mass is delayed, or interrupted, according to the degree 

 of damage. These and other ingenious experiments overthrew those 

 hypotheses which held the nerve cells in high relief, and gave the lead to the 

 work which followed ; for it was assumed, in the light of his experiments, 

 that the contraction travels throughout the heart as a wave from one chamber 

 to the next and that it is carried across the gaps by means of muscular 



