272 Bayliss and Starling, 



As the heart dies, the block between auricle and ventricle ra- 

 pidly increases, till at last it becomes complete, and no transmission 

 of excitation from auricle to ventricle takes place. In one case, in 

 which we measured this period of time in the excised heart in the 

 warm chamber immediately after removal from the body, we found 

 that the excitatory change took 0.30" to travel from auricle to base 

 of the ventricles. 



Velocity of propagation in ventricle. 



Sanderson and Page showed that the velocity of propagation of the 

 electrical change in the frog's ventricle, might be measured by the 

 time-interval between the beginning and culmination of the initial 

 phase of the variation. Our observations on Mammals have shown, 

 however, that in warm-blooded animals the duration, and indeed the 

 very existence of this initial phase, are so extremely susceptible to 

 slight changes of temperature that no measurement of it could be re- 

 lied on as giving the real time taken in the passage of the excitatory 

 change from base to apex of the ventricle. Probably we should obtain 

 a more accurate estimation of this time-interval in intact animals, 

 where the conditions as to temperature are constant, (see Appendix.) 



For examples of the kind of curves obtained in these measure- 

 ments, see Plate XVI. figs. 17 to 21. 



No definite conclusions as to the nature of the transmission from 

 auricle to ventricle can be drawn from these results. It may be said 

 that the loss of time at the gi-oove, and the fact that transmission is 

 possible in either direction across the groove, point to a direct muscu- 

 lar continuity. Anatomists, however, state the contrary, but until a 

 careful series of sections has been made, the point cannot be con- 

 sidered decided. There is, moreover, the possibility of a nerve-network 

 of a rudimentary kind, and we must not be too dogmatic as to the 

 impossibility of such a network taking up excitation at any point and 

 transmittnig it to any other point. That nerve-fibres of the ordinary 

 kind are not the means of transmission is, we think, shown by our 

 results. 



