-512 



Mr. K. Lucas. 



[June 6, 



the disturbance from the seat of excitation to the normal region. However, 

 Hartl's experiments were made on thin muscles which had been for half an 

 hour in the non-isotonic solutions, and such a source of error is therefore 

 improbable. 



Quite recently new evidence along the same lines has been brought to light 

 by the work of Noyons* on the electric response of the heart. Working on 

 the hearts of frogs, tortoises, and fresh-water mussels he has found that 

 various drugs will abolish the beat in so far as it consists of contraction, 

 while leaving the rhythmic electric response still strong. If in these 

 hearts the disturbance is propagated along the muscular tissue, then the 

 presence of the electric response in parts of the heart not contracting 

 and not excited from without seems to be clear evidence that the propagated 

 disturbance has passed over the muscle without any accompanying con- 

 traction. Miiiesf has also just reported a case of this dissociation. The 

 skeletal muscles of the ray after treatment with a dilute solution of ether 

 give no mechanical response to strong interrupted electric currents, but 

 still contract fully when bathed with suitable concentrations of acid, alkali, 

 or potassium salts. In this case the order of things is reversed, the 

 mechanism of excitation and propagation being apparently thrown out of 

 gear while the mechanism of contraction is still present. On quite different 

 lines he has argued for the dissociation from the effects of certain ions on 

 the heart. A hydrogen ion concentration slightly above that normally 

 encountered by the heart will cause stoppage in the relaxed state ; a still 

 higher concentration produces permanent contraction. The separation of 

 these two stages of action is emphasised by the fact that trivalent cations 

 can produce the former but not the latter. He suggests that the first stage 

 means a stoppage of the processes concerned in excitation and propagation, 

 while the latter indicates that in the meantime the mechanism of contraction 

 has not been damaged. 



All this evidence tends in the same direction, that of showing the contrac- 

 tion process to be not an essential part, but a consequence of the propagated 

 disturbance, following that disturbance only in those tissues in which the 

 necessary mechanism is present. 



E. The Liberation of Heat. 

 The last of all the chain of processes which 1 am attempting to bring- 

 within this analysis is the liberation of heat. Happily, since we are now 

 concerned only with relating this process to the propagated disturbance, the 



* Noyons, ' K. Akad. v. "Wet. te. Amsterdam,' November, 1908, and April, 1910. 

 t Mines, ' Proc. Physiol. Soc.,' May 18, 1912. 



