278 Dr W. H. Gaskell, On certain points [Nov. 27, 



special ganglionic apparatus to conduct the contraction from sinus 

 to auricle or from auricle to ventricle, for in both the frog and 

 the tortoise a band of circularly disposed muscular fibres exists 

 at the sino- auricular and auriculo-ventricular junctions, through 

 which the contraction wave is able to pass from sinus to auricle 

 and from auricle to ventricle respectively. 



Further the resemblance between the artificial blocking of the 

 contraction wave by means of section to the natural block at the 

 sino-auricular and auriculo-ventricular junctions was pointed out, 

 and it was shown that the pauses between the contractions of the 

 several cavities of the heart could be ascribed to the nature of the 

 muscular tissue at these junctions together with the anatomical 

 arrangement of the fibres there. 



The ultimate conclusions therefore obtained from those parts 

 of these three papers which dealt with the beat of the heart are 

 the following : 



1. The beats of the heart represent a series of separate peri- 

 staltic contractions which start from the sinus end and pass iu 

 regular order over the whole heart. 



2. The peristaltic nature of these contractions is obscured by 

 the fact that the wave of contraction passes along a muscular tube 

 which is not of the same diameter or structure throughout ; so 

 that the contractions of certain portions, which by bulging have 

 become more prominent and by a higher development of structure 

 have become more rapid in their contraction, are so pronounced 

 as to give the impression of separate contractions of these pjrtions 

 with pauses between them. 



3. The conduction of this wave of contraction can be arti- 

 ficially hindered by various methods in any part of its course ; 

 so that if the hindrance is but slight an artificial pause is pro- 

 duced, if greater a partial block, in which case every second con- 

 traction passes the block, if still greater an increasing block until 

 at last the block is complete and no contraction-wave is able to 

 pass. 



So far I have but slightly touched upon one most important 

 point in this conception of the heart's rhythm, viz. the nature of the 

 starting point of this contraction-wave. It is the consideration 

 of this point to which I desire to call attention in this part of 

 the present paper. 



In the frog the septum between the two auricles plays an 

 important role in all discussions upon the nature of the rhythmical 

 contractions which occur after the removal of the sinus. In the 

 tortoise on the other hand the septum possesses no such importance, 

 its place is taken by a band of tissue, which passing from the 

 sinus to the ventricle connects the two auricles together and is 

 the path along which the coronary veins and the nerve trunks 



