200 



Dr. W. H. GaskelL 



[Dec. 22, 



its contractions ; while on the other hand, when applied to the 

 auricles and sinus alone, it quickens the rhythm most markedly 

 Cold, atropin, muscarin, all slow the rhythm when applied to auricles 

 and sinns, but cause no alteration of rhythm except in extreme doses 

 when applied to the ventricle alone. 



The author then proceeds to consider the conditions which are 

 necessary in order that each one of these impulses should produce a 

 contraction, and concludes that a due relation must exist between the 

 strength of the impulse and the excitability of the tissue in order to 

 obtain this result. 



By a comparison of the rate of the contractions of the auricles with 

 those of the ventricle, it is found that the ventricle can be made to 

 beat synchronously with every second, third, fourth, or more auricular 

 beats, or to cease from beating altogether by increasing the com- 

 pression of the clamp in the auriculo-ventricular groove or by heating 

 the sinus and auricles alone without heating the ventricle. The com- 

 monest and most permanent effect is to make the ventricle beat 

 synchronously with every second auricular beat. 



This same want of sequence between the ventricular and auricular 

 contractions can also be obtained by the application of various poisons 

 to the ventricle alone. A marked difference however exists between 

 the two cases. In the first case, when the ventricle is made to beat 

 with half-rhythm by tightening the clamp, or by heating the auricles 

 and sinus, its contractions are those of a strong vigorous muscle, and 

 are more powerful than when the ventricle was beating synchronously 

 with every beat of the auricles ; on the other hand, the application of 

 poisons to the ventricle does not produce this effect on its rhythm 

 until by the action of the poison the force of the contractions has 

 become greatly reduced. 



For this and other reasons given in the original paper, the author 

 concludes that either tightening the clamp or heating the auricles and 

 sinus alone diminishes the strength of the impulses passing to the 

 ventricular muscle, and so causes the half-rhythm observed ; while 

 various poisons applied to the ventricle alone produce the same effect 

 by diminishing its excitability, without affecting the strength of the 

 impulses. 



The conclusions arrived at in Part I can be summed up in the 

 following propositions : — 



1. The rhythm of the heart is caused by discrete motor impulses 

 passing to the muscular tissue from certain motor ganglia. 



2. In order that each one of these impulses may produce a con- 

 traction of the ventricle a due relation must exist between the 

 strength of the impulse and the excitability of the ventricular muscle. 



3. When each impulse is inefficient to cause a contraction of the 

 ventricle, the ventricular muscle has the power of summing up the 



