274 Bayliss and Starling, 



clearly marked on the flat part of the photograph between the heart 

 beats as on the curve of the variation caused by each heart beat — 

 unless we are to take these vibrations as shewing the existence of a 

 tetanic relaxation of the mammalian heart. 



3. Frédéricq however lays most stress on the three-topped curve 

 obtained from dying hearts, or rather from hearts just before they go 

 into a condition of delirium. The fact that these curves are mono- 

 phasic shews that one of the leading-off points must have been injured. 

 In the next section we shall consider certain forms of curves which 

 we call „stepped" cui'ves, and which are obtained when one of the 

 leading-off points is injured. The examples we give ai'e very similar 

 to the two-topped curves given by Frédéricq. We have also obtained 

 three-topped curves in some cases, in which the heart, which had 

 been beating regularly and giving a two-topped or stepped curve, 

 suddenly gave two or three double beats. Just before the heart goes 

 into delirium, it beats extremely irregularly, the beats often consisting 

 of pairs of partially fused contractions; and we feel inclined to ascribe 

 a like origin to the three-topped curves of Frédéricq. 



But in whatever way we explain these curves, we do not feel 

 that one is justified in drawing conclusions as to the nature of the nor- 

 mal beat from the electrometer-curve of the electrical variation of a 

 dying and injured heart on the point of going into delirium cordis. 



IV. , 



' It remains to mention a few facts relating to the effects of in- 

 jury on the form of the electrical wave. As shewn by Sanderson and 

 Page, the effect of injury of the muscular substance at either of the 

 points led off, is to diminish or abolish the excitatory state at that 

 point, hence leading to the production of a monophasic electrical va- 

 riation when the excitatory state is quite abolished at one contact, or to 

 various forms of what we may call „stepped" curves when it is di- 

 minished. The monophasic electrical variation is the expression of the 



