172 



THE CONTRACTION OF CARDIAC MUSCIE. 



or discontinuous impulses passed from the sinus to auricle and ventricle, 

 could be easily answered by increasing the excitability of ventricle or 

 auricle respectively. A more excitable ventricle must respond to a 

 constant stimulus with contractions at a more rapid rate than a less 

 excitable one ; while, on the other hand, the rate would remain unaltered 

 if the impulses from the sinus were discontinuous, and the excitability 

 of the ventricle only were altered. 



For this purpose I made use of a method of registering the heart contrac- 

 tions which up to that time had not been used, and has since proved of 

 great value ; this method is the suspension method. The contraction of the 

 auricle and ventricle are registered separately by means of two levers, which 

 are attached by means of threads to the apex of the ventricle and auricle 

 respectively ; the one lever is pulled downwards against an elastic spring, and 

 the other upwards. The heart is held fast by means of a screw-clamp in the 



Fig. 101. — Frog's heart. Suspension method. Clamp in auriculo- ventricular groove. 

 Auricles and sinus above clamp, ventricle below. Coil round auricles and sinus ; heated 

 between the vertical lines. The ventricular contractions at first keep pace with the 

 quickening auricular, then are unable to do so, and at a the ventricle contracts to 

 every second of the auricular contractions. 

 » 

 auriculo-ventricular groove. This clamp is provided with a line screw, which 

 can easily be adjusted so as to hold the heart firmly, without injuring the 

 tissue. In this way the contractions of auricle and ventricle can be registered 

 separately. 



The excitability of a tissue can be increased by raising its temperature up 

 to a certain limit. In my experiments I made use of a coil of thin wire, which 

 was heated by the passage of a galvanic current through it. This coil was 

 placed so as to surround either the auricles and sinus or the ventricle, so that 

 in this way the auricular or ventricular side of the heart could be heated 

 separately. Curves so obtained are given in Figs. 101 and 102, taken from my 

 paper in the Philosophical Transactions, 1 and it is seen that, whereas heating 

 the auricles and sinus causes a great increase in the rapidity of the beats both 

 of auricles and ventricle, no alteration of rate of rhythm in the ventricle is 

 produced by heating the ventricle alone, but the force of its contraction 

 is altered. 



1 "On the Rhythm of the Heart of the Frog and the Nature of the Action of the Vagus 

 Nerve," Phil. Trans., London, 1882, p. 993, Figs. 1 and 2, PL lxvii. 





