Mechanism and Control of Fibrillation in Mammalian Heart, 303 



made by {a) the myocardiograph, used in the same way as with the heart 

 in situ, and (h) by a rubber bag placed in the left ventricle and connected 

 with a Hiirthle manometer, the system being filled with liquid. All the 

 tracings are to be read from left to right ; they are all ventricular (L.V. 

 of cat) records except where otherwise noted.* The time is shown in seconds. 



For the more accurate use of faradic currents, a Kronecker's inductorium 

 was employed, with two volts in the primaiy circuit ; the values of the 

 units stated are to be taken as obtained with this E.M.F. in each case. For 

 obtaining series of shocks at different rates, a Brodie cut-out arrangement 

 was used, giving either make or break shocks at regular intervals ; these 

 shocks were recorded on the tracings by an electrical signal. The shocks 

 were often applied through the myocardiograph, so that they traversed a 

 considerable amount of the cardiac substance ; at other times they were sent 

 through electrodes about 1 mm, apart, etc. 



The Conduction of the Eoccitation in Fibrillation. 



Instead of travelling uniformly right through the mass of muscle without 

 evident regard to the direction of the fasciculi or bands of muscle, as under 

 normal conditions, the excitation wave in fibrillation travels most easily 

 along the complexly-arranged fasciculi, there being an impairment or 

 failure of propagation at most of the inter-fascicular connections. Such 

 a mode of propagation of the rapidly-recurring contraction waves may be 

 clearly perceived on direct inspection of the heart, and on palpation of the 

 ventricles the apical portion being held between the finger and thumb with 

 varying degrees of light pressure. In the latter case, instead of the normal 

 uniform hardening of the muscular wall at systole, there is a striking want of 

 synchronism in the hardening of the constituent fasciculi, short contraction 

 waves in rapid succession hardening different sets of fibres, while others are 

 relaxed and soft, the contracted ones momentarily standing out and giving a 

 characteristic " wiry " feeling among the quiescent fasciculi ; the impression of 

 an incessant turmoil of dissociated or in-coordinated activity is a vivid one. 

 The myocardiograph record shows a series of rapid irregular oscillations, 

 varying to some extent from place to place in rate and in range of excursion. 

 Similar records are obtained from the perfused heart. 



The failure of normal conduction may be induced in two ways : (1) by 

 depressing agencies acting directly on conductivity, and causing more or less 

 extensive blocking in the most susceptible parts, the inter-fascicular 

 junctions, while the intra-fascicular connections remain functional. This 

 effect may be produced even with a moderate or slow succession of 

 * Upward movement of the ventricular lever = systole. 



2 B 2 



