THE MEANING OF THE HEARTBEAT. 171 



would beat rhythmically, provided that there was sufficient tension of 

 its walls. 1 The importance of the tension of the walls in the production 

 of rhythmical contractions of the apex of the heart was also, about the 

 same time, insisted on by J. M. Ludwig and Luchsinger, 2 who showed 

 that the rate of rhythm was closely associated with the pressure within 

 the cavity. 



From these experiments the conclusion followed, that the muscular 

 tissue of the heart was of such a character, that a sufficiently powerful 

 constant stimulus, whether electrical, chemical, or mechanical, did not 

 produce a constant tonic contraction, but was manifested as a rhythmical 

 series of contractions. 



The net result of these facts upon the minds of the upholders 

 of the motor ganglia theory was to cause them to put forward the 

 proposition, that the impulses sent out by the centre in the sinus were 

 not discontinuous but continuous, and that the cardiac muscle re- 

 sponded to this continuous stimulation by a rhythmical contraction. 



Pari passu with the question of the meaning of the cardiac rhythm 

 goes the question of the sequence of the contractions of the different 

 parts of the heart, and here again we see the ganglion cells conspicu- 

 ously pressed into service. The original view held by Haller, and 

 others of his time, was that a peristaltic wave of contraction passed 

 over the heart from the great veins to the aorta. This conception of 

 a peristaltic muscular wave was given up largely, because it was noticed 

 by Schiff and others that the ventricle of the dying heart frequently 

 beats at a different rate from that of the auricle ; it was therefore 

 asserted that such a phenomenon could not be due to a peristaltic wave, 

 but showed that a co-ordinating mechanism of a presumably nervous 

 nature had got out of gear, and therefore the ventricle no longer 

 responded in due sequence to the auricle. 



This co-ordinating mechanism was held to be situated in the 

 cells of Bidder's ganglia, in consequence mainly of the experiments of 

 Eckhard 3 and Marchand, 4 which appeared to indicate that the sequence 

 of the contraction of ventricle upon that of auricle depended upon 

 the integrity of these ganglia ; also, that the time which elapsed 

 before the ventricle contracted upon stimulation of a point in the 

 auricle was too long for the passage of a wave of muscular contraction ; 

 this greater length of time must therefore be explained by a delay 

 caused by the passage of the impulse through a special nerve centre — 

 in other words, through Bidder's ganglia. 



So far, then, the conception formed was: — Motor ganglia in the sinus 

 send out a continuous impulse along nerve fibres to auricle and ventricle ; 

 such impulse produces a discontinuous rhythmical result, owing to the 

 nature of the muscular tissue ; the sequence of the contraction of the 

 ventricle upon that of the auricle is due to a delay in the impulse, 

 owing to its passage through the ganglia at the auriculo- ventricular 

 junction. 



Such was the condition of things when I commenced my investiga- 

 tions in 1881, and it seemed to me that the question whether continuous 



1 "On the Tonicity of the Heart and Blood Vessels," Journ. Physiol, Cambridge and 

 London, 1880-82, vol. "in. p. 51. 



- Med.-chir. Gentralbl., AVien, 1879, S. 404; Arch. f. d. gcs. Physiol., Bonn, 1880, 

 Bd. xxv. S. 211. 



3 Beitr. z. Anat. u. Physiol. {Eckhard), Giessen, Bd. vii. S. 191. 



4 Arch. f. d. gcs. Physiol., Bonn, 1878, Bd. xvii. S. 137. 



