[mines] CIRCULATING EXCITATIONS IN HEART MUSCLES 49 



connexion. It is possible then that the ventricle would excite the 

 ventricular end of this right lateral connexion, not finding it refractory 

 as normally it would at such >a time. The wave spreading then to the 

 auricle, might be expected to circulate around the path indicated. 

 But if the recovery of the main A-V connexion or of the ventricle itself 

 was not sufficiently rapid, the circulating wave could not continue 

 and what would be observed would be a series of groups of this type 



aur.-ventr.-aur. aur.-ventr.-aur aur.-ventr.-aur. etc. 



a type of rhythm known to occur both under experimental conditions 

 and in disease. 



We know enough of the physiological properties of heart muscle 

 and the arrangement of the fibres in the human heart to enable us to 

 speak of a circulating excitation between auricles and ventricles 

 as a theoretical possibility and to say that if it did occur, auricles and 

 ventricles would beat at a much more rapid rate than normal and 

 that the onset and the disappearance of the abnormal rhythm would 

 be abrupt. 



Fibrillation. 



The suggestion that the abnormal character of the heart's activity 

 in fibrillation depends essentially on abnormality of conduction was 

 put forth by W. T. Porter in 1898. Porter's view has recently re- 

 ceived very strong support from the experiments of Garrey, 1 to whose 

 admirable paper I would refer the reader. Garrey points out that 

 fibrillation is more easily aroused and is more persistent in large than 

 in small pieces of heart muscle and he shows that it is most unlikely 

 that the self-maintained activity in fibrillation is due to an exaggerated 

 power of ectopic impulse formation. Garrey arrives independently 

 at a closely similar conclusion to that which I expressed in a recent 

 paper, 2 namely, that fibrillation is due to waves travelling in closed 

 circuits in the syncytium. 



Garrey observes that if the above conclusion is correct, it is not 

 surprising to find the onset of fibrillation induced by such conditions 

 as local differences of temperature or the application of certain drugs 

 which may reach one region sooner than another. Professor Starling 

 has mentioned to me that in the course of his numerous experiments 

 on heart-lungs prepared from the dog, a detail of technique which he 

 found of some importance was to avoid touching the surface of the 

 heart with a cold instrument, since this was found very frequently 

 to start fibrillation. 



The most certain method of starting fibrillation is by the appli- 

 cation of a faradic current directly to the heart. The rapid series of 



1 Garrey. Amer. Journ. Physiol. 33. p. 397. March, 1914. 



2 Mines, loc. cit. 



