Section IV., 1914 [43] Trans. R.S.C. 



On circulating excitations in heart muscles and their possible relation to 

 tachycardia and fibrillation. 



By Prof. George Ralph Mines. 1 



From the Station Biologique, Roscoff, France, and the Physiological 

 Laboratory of the University of Toronto. 



Presented by Prof. T. G. Brodie, F.R.S.C. 



(May 27, 1914.) 

 § 1 The propagation and duration of the excited state in heart muscle. 



If a strip of heart muscle, living but not exhibiting spontaneous 

 activity, is touched at one end with the point of a needle, an altered 

 state is aroused at the point stimulated which is rapidly propagated 

 over the strip. This altered state, the "excited state," is characterised 

 essentially in two ways — by a difference of electrical potential between 

 the part of the tissue in the excited state, and a part not excited and 

 by the inability of the tissue to respond to a second stimulus (absolute 

 refractory period) . The onset of the excited state is normally followed 

 very shortly by a mechanical movement, which continues as con- 

 traction until the excited state disappears and then gives place to 

 relaxation. 



The relation between the mechanical response and the excited 

 state is such that the former can, under certain conditions such as the 

 removal of calcium, be abolished while the latter remains. Con- 

 traction is not an essential part of the excited state. 



The excited state is propagated in the ventricle of the frog or the 

 tortoise at room temperature at the rate of about 10 cms. per second, 

 while it persists at any one point a considerable time, e.g. 1" or 2". 

 Thus if the strip is only 3 or 4 cms long, the excited state will still be 

 present at the point stimulated when it has reached the other end of 

 the strip, and for a time the whole strip will be in the excited state. 

 In other words the wave of excitation is longer than the strip of tissue. 

 But if now a second stimulus is applied so as to start a second wave 

 in the tissue as soon as possible after the su bsidence of the first wave 



1 Owing to the sudden death of the Author before this paper was printed, the 

 proofs have been read by Dr. T. G. Brodie, who desires to be held responsible for 

 the corrections. 



