NUTRITION OF THE HEAR T. 227 



regular rhythm, is due to some alteration in the rhythmical organ itself. In 

 all these experiments the contractions of the ventricle alone are registered, the 

 auricular contractions being only registered occasionally by the accident of 

 their appearance on the ventricular curve. It is therefore not clear to my 

 mind how far these groups of ventricular beats may be due to the passage of 

 a series of contractions into the ventricle over a blocking-place, somewhere 

 between the starting-place of the rhythm and the ventricular tissue. 



Certainly I have occasionally obtained, by means of tightening the clamp 

 in the auriculo- ventricular groove, a series of ventricular contractions which for 

 a time were arranged in groups just like Luciani's groups, and Fano mentions 

 the same thing as the effect of clamping. The separate ventricular contrac- 

 tions in these groups usually corresponded to every second contraction of 

 the auricle, though occasionally a few contractions were able to respond to 

 every auricular contraction, so giving curves resembling some of those figured in 

 Langendorffs paper. In fact, during the group the conductivity of the tissue 

 at the blocking point altered from that of a complete block to that of a partial 

 block. Again, one of the most striking phenomena observed and recorded by 

 me in my paper in the Philosophical Transactions, was the manner in which 

 the vago-sympathetic nerve was able to cause a group of ventricular contrac- 

 tions, when, by means of heating or clamping, a complete block had been formed 

 between auricle and ventricle. This group of contractions was most clearly 

 dependent on the auricular contractions, being either all synchronous with 

 those of the auricle, or mostly synchronous, with a few at the beginning or 

 end of the group synchronous with every second auricular contraction. When 

 we remember also that it is very difficult, without most careful investigation, 

 to be sure that the sinus is not beating regularly when the heart is apparently 

 still, that Luciani and Kossbach tied on to the cannula, not the ventricle alone, 

 but the whole heart, and that it is astonishing how tightly it is necessary 

 to screw up a clamp (or in their case to tie a ligature) between auricle and 

 ventricle, so as to cause a block sufficiently complete to prevent the effect of 

 the stimulation of the vago-sympathetic nerve, it is, I think, more probable 

 than not that the so-called Luciani's groups, or periodic beating, owe their origin 

 to a partial blocking of the contraction wave into the ventricle, and not to a 

 peculiar periodicity of rhythm. Such an explanation is in complete harmony 

 with the view that a condition of asphyxia is most favourable for the pro- 

 duction of these groups, for such a condition is certain to produce a greater 

 or less amount of blocking. 



