When the heart is tied on to a cannula in the same way as the apex, by a ligature round the auricles or even the sinus, so that, instead of containing no ganglia at all, it contains either Bidder's or Bidder's and Remak's ganglia, it also remains motionless in the same way as the apex when supplied with chloride of sodium solution, but its rhythmical power is restored by the addition of defibrinated blood, of serum, of solution of the ashes of serum, by a trace of Na2CO3, or still better by the addition of .005 per cent. of NaHO and a trace of peptone or serum-albumin. When supplied with pure serum, it does not beat regularly, but its pulsations occur in groups separated by long intervals (Fig. 104) .3 When a little haemoglobin or blood is added to the serum, this grouping disappears, and the pulsations become regular.1

Fig. 103.   Diagram to show the difference in the mode of experimenting with the heart and with the apex alone. In a the apex alone is attached to the cannula.

Fig. 103. - Diagram to show the difference in the mode of experimenting with the heart and with the apex alone. In a the apex alone is attached to the cannula. In 6 the heart, consisting of ventricle and auricles, or of the venous sinus also, is attached to the cannula.

1 Ringer, Practitioner, vol. xxx. p. 17.

2 Hermann's Handb. d. Phys., iv. 1, p. 357.

3 Luciani, Ludiuig's Arbeiten, 1872, p. 120.

When the heart has been supplied with haemoglobin or blood and is beating regularly, the addition of a little veratrine causes the groups to appear, and a similar effect is produced if the blood is not renewed, but allowed to remain in the heart till it becomes venous.2

Fig. 104.   Periodic rhythm of the heart, the pulsations occurring in groups separated by intervals of complete quiescence.

Fig. 104. - Periodic rhythm of the heart, the pulsations occurring in groups separated by intervals of complete quiescence.

This periodic stage does not occur immediately after the heart has been tied on the cannula and supplied with serum. It is preceded by an initial stage, in which the beats are at first very quick, then slow, and these are separated by long pauses. Next comes the periodic stage in which the groups occur. It is succeeded by the stage of crisis in which the groups are replaced by single pulsations slower and smaller than the normal.

Atropine and nicotine do not prevent the occurrence of groups. Both of them make the groups longer and the pauses shorter. Atropine, however, even in small doses, soon kills the heart before it even enters on the stage of crisis. Nicotine, on the other hand, shortens the pauses, and rapidly induces the stage of crisis without destroying the energy of the heart, which is quite as great after poisoning by nicotine as in the normal condition.

Moderate doses of muscarine make the pulsations smaller and slower, the groups shorter, and the pauses longer. Sometimes the heart becomes exhausted before the stage of crisis appears, at other times it does not. Large doses of muscarine arrest the movements of the heart.

The activity of the heart which has been stopped by muscarine is again restored by atropine, but muscarine can render the beats smaller and slower, even after the previous application of atropine.

The occurrence of groups appears to be most probably due to interference of rhythms - of the ganglionic rhythm with that of muscular fibre.

We find an indication of alternate interference and coincidence of two rhythms in the alterations which sometimes occur ; in the beats of a ventricle containing its ganglia, but separated | from the auricles. At first all the beats are of equal strength, but soon each alternate beat gets longer and shorter, till some disappear and others get much stronger than before (Fig. 105 ; cf. Fig. 64, p. 168).

1 Rossbach, Ludwig's Arbeiten, 1874, p. 92.

2 Ibid., p. 93.