SEQUENCE OF CONTRACTION OF PARTS OF HEART. 183 



Marchand, 1 in the muscular tissue of the ventricle of the frog, which they 

 estimated as greater than 20 mm. per second. 



If it be necessary still further to prove that the sequence of the ventricular 

 upon the auricular contraction has nothing to do with the presence of ganglion 

 cells at the auriculo- ventricular junction, it may be mentioned that the removal 

 of the auriculo-ventricular ring in the tortoise t bit by bit shows that those 

 parts of the ring which contain ganglion cells in largest quantity, namely, the 

 parts where the large nerves enter the ring, are not so efficient in maintaining 

 the sequence of the contractions as those parts near the aorta where ganglion 

 cells are comparatively scanty. It is also evident that the experiments which 

 have been relied upon as strongly suggesting a co-ordinating centre for the due 

 sequence of ventricular and auricular contractions, can be explained on the 

 theory of blocking of a muscular wave of contraction. The three principal 

 arguments used are 



1. Schiff s observation, that in the dying heart the ventricle beats more 

 slowly than the auricle, and therefore the contraction is not of the nature of a 

 peristaltic wave. The phenomena of the apparent independence of the beats 

 of the various heart cavities during the process of dying are all beautiful 

 illustrations of a gradually increasing block, first at the auriculo-ventricular 

 junction, and then at the sino-auricular. 



2. Eckhard's 2 observation that section of the septum together with its nerves 

 in the frog causes the ventricle to beat independently of the auricle. In this 

 case the slower beat of the ventricle observed by Eckhard was clearly not 

 independent of the auricular beat, for he himself says that both auricular and 

 ventricular contractions were stopped by stimulation of the vagus nerve, 

 although the nerves of the septum were cut ; plain proof that the ventricular 

 rhythm in his experiments was not independent of the auricular, and that in 

 cutting through the septum he had damaged the auriculo-ventricular muscular 

 ring, and so caused a partial block. 



3. Marchand's 3 observation, that the time taken before the ventricle 

 contracts when a stimulus is applied .to the auricle is too long to be accounted 

 for by the travel of a wave of contraction along muscular tissue ; the delay he 

 accounted for as due to processes going on in Bidder's ganglia, and to prove 

 this he removed Bidder's ganglia, and then found the sequence gone. The 

 first part of Marchand's proof is based on the erroneous assumption, that the 

 rate of travel in the muscular tissue from auricle to ventricle is the same as 

 that shown by Engelmann's observations in the ventricular muscle, whereas 

 we have seen that the low conducting power of the auriculo-ventricular 

 muscular ring is quite sufficient to explain Marchand's figures. As to his 

 second argument, it is very difficult to remove Bidder's ganglia without 

 seriously damaging the auriculo-ventricular muscular ring, especially if, as in 

 Marchand's case, the attention is not particularly directed towards this ring. 

 I have, however, succeeded in doing so, and found, 4 as indeed did Bidder 

 himself, no alteration of sequence whatever as the result of such removal. 

 I conclude, therefore, that Marchand, as well as Eckhard, caused a block by 

 damage to the auriculo-ventricular ring when he removed the two ganglia. 



This, then, is the explanation of the sequence of the contractions. 

 A rhythmical series of contractions start from the sinus, traverse the 

 heart as peristaltic waves, and come out at the bulbus arteriosus ; and 

 with such an explanation one thing clearly follows such contractions 

 must pass over the heart, whether they start at one end or the 



1 Arch.f. d. ges. Physiol., Bonn, 1878, Bd. xvii. S. 137. 



- Beiir. z. Anat. u. Physiol. (Eckhard), Giessen, Bd. vii. S. 191. 



3 Arch.f. d, ges. Physiol., Bonn, 1878, Bd. xvii. S. 137. 



4 Journ. Physiol., Cambridge and London, 1883, vol. iv. p. 75. 



