1 70 THE CONTRA CTION OF CARD I A C MUSCLE. 



In both cases Rosenthal ascribed the rhythmical activity to the automatic 

 action of groups of easily excitable nerve cells. In the case of respiration, these 

 cells were those governing the movements of the ordinary muscles of inspira- 

 tion ; in the case of the heart, the cells in the sinus venosus. In both cases, 

 additional, subsidiary, less excitable centres were assumed to exist, which re- 

 quired a stronger stimulus to make their presence manifest ; such centres were, 

 in the case of respiration, the centres connected with the extraordinary muscles 

 of respiration, which were thrown into activity by increasing venosity of the 

 blood ; and in the case of the heart, Bidder's ganglia in the auriculo-ventricular 

 groove, which, though normally inactive, were capable of being aroused by a 

 sufficiently strong stimulus. The first Stannius ligature, or cut, at the junction 

 of sinus and auricles, caused standstill, according to this view, because it 

 removed the automatic motor centre or Remak's ganglia ; the second Stannius 

 ligature, in the auriculo-ventricular groove, caused the ventricle to beat again, 

 because it supplied the extra stimulus necessary to set in action the less excit- 

 able motor cells of Bidder's ganglia. 



Such, then, was the conception of the heart-beat. A motor centre 

 was supposed to exist in the sinus, which was usually active, thus 

 resembling the ordinary centre for respiration, and which sent out dis- 

 crete impulses to the muscular tissue of the auricles and ventricle. This 

 centre was supposed to be supplemented by a less excitable motor centre 

 between auricle and ventricle, which was normally inactive, but avail- 

 able, like the extraordinary centres of respiration, for employment upon 

 an emergency. 



This view soon began to receive modification, when, in consequence 

 of the experiments of Eckhard x and Foster and Dew Smith, 2 it was 

 proved that the ganglion-free apex of the frog's heart was thrown into 

 rhythmical activity by the passage of a constant current through it, and 

 also that this same apex would beat rhythmically when supplied with a 

 nutrient fluid under pressure, as proved by the experiments of Bow- 

 ditch 3 and Merunowicz 4 in Ludwig's laboratory. 



These experiments were proof positive that, under certain conditions, 

 the muscular tissue of the heart would beat rhythmically without 

 the presence of motor nerve centres. It was however argued, that such 

 rhythmical contractions had nothing to do with the normal beating of 

 the heart, but were due to the foreign stimulus of the electrical 

 current on the one hand, and of the chemical ingredients of the 

 nutritive fluid on the other ; and Bernstein 5 showed, by clamping the 

 ventricle between the base and apex, that if the apex were cut off from 

 the base, then, although kept still supplied with blood from the con- 

 tractions of the base, it yet remained motionless, and never contracted of 

 itself. In other words, the stimulus of its own blood was not sufficient 

 to arouse rhythmical contractions in the apex of the frog's ventricle. 

 Bernstein, however, did not realise the importance of another factor in 

 the causation of rhythm in the isolated apex, namely, the pressure in its 

 cavity ; and at Foster's suggestion I was able to show, by clamping 

 the aorta, and so increasing the pressure in the cavity of the ventricle, 

 that the apex of the frog's heart, when isolated after Bernstein's method, 



1 Beitr, z. Anal. u. Physiol. (Eckhard), Giessen, 1858, Bd. i. 



- Journ. Anat. and Physiol., London, 1S76, vol. x. 



3 Per. d. k. Sachs. Gesellsch. d. Wissensch., Leipzig, 1871, S. 682. 



i Ibid., 1875, S. 254. 



5 Centralbl. f. d. med. Wissensch., Berlin, 1876, S. 385. 



