86 



during muscular effort, but often apart from this, in the 

 absence of recognizable exciting cause or in presence of 

 causes too trivial to have any effect under ordinary con- 

 ditions. And, apart from sudden obstruction, there is no 

 reason to doubt that a gradual interference with the blood 

 supply as a result of coronary disease can, by damaging 

 the nutrition and altering the properties of the muscle, 

 lead to an abnormal susceptibility to fibrillation. 



The applicability to man of these results is naturally easy 

 in view of the widespread tendency to serious impoverish- 

 ment of the blood supply (local or general) of the cardiac 

 muscle in the later half of life, the period when deaths of 

 the class under consideration usually occur. In the light 

 of these facts we have a rational basis for many unexplained 

 disasters — fatal events that otherwise remain shrouded in 

 mystery. 



While the effects of limitation of the blood supply are 

 proved by abundant and convincing evidence, other 

 agencies, such as perverted nutrition, toxic influences, 

 generative changes, etc., can be effective causes. Inter- 

 ference with normal functioning of the Purkinje fibres on 

 the inside of the ventricles comes into question as well as 

 alterations in the ordinary myocardium. Fibrillation may be 

 determined at a certain point of time by a sudden aggrava- 

 tion or cumulation of the toxic condition, etc., aided, it 

 may be, by the incidence of some disturbance of the vas- 

 cular system too slight to produce any serious effects except 

 in the specially predisposed condition. 



It is to be borne in mind that the conditions disposing 

 to and leading up to fibrillation need not pervade the whole 

 of the ventricular musculature, but may be limited to a 

 certain amount of that tissue, as after obstruction of a 

 coronary branch and in other conditions; changes in 

 restricted areas can set up fibrillation, which involves the 

 rest of the muscle, healthy as the great bulk of it may be. 

 It is readily intelligible that such limited changes may 

 naturally be associated with little or no recognizable altera- 

 tion in the force of the ventricular beat or its general 

 efficiency. Thus there may be little or no warning of the 

 impending catastrophe, even at a time when the mine has 

 been laid and only a spark is needed to precipitate the 

 explosion. 



Ahnormal Cardio-vascular Variations of Obscure Origin. 



Under certain conditions of cardio-vascular instability — 

 usually occurring in association with morbid states of the 

 arterial system — irregular tides of circulatory change, often 

 obscure as regards their exciting causes, are sometimes recog- 

 nizable; one manifestation of these is found in the exten- 

 sive variations of arterial pressure as measured under 

 similar conditions from day to day or at shorter intervals. 

 These variations are sometimes, but not necessarily, 

 associated with discrepancies in the sphygmomanometer 



