196 THE CIRCULATION OF THE BLOOD 



the central nervous system, so that the method of applying stronger cur- 

 rents, even were it feasible to do so quickly enough, would be of no 

 therapeutic value in removing fibrillation. 



The disappointing results that have followed the repeated attempts 

 to resuscitate persons killed accidentally by electric shocks is undoubt- 

 edly dependent upon the fact that in the heart of man it is impossible 

 to bring back the normal beat after the ventricles have been thrown into 

 fibrillation. Fibrillation of the ventricle is also the cause of the sudden 

 cardiac failure occurring when blood clots or emboli cause a blockage 

 of the coronary circulation (it is sometimes the cause of angina pec- 

 toris, for example). It must also be remembered in clinical practice 

 that mechanical stimulation of the ventricles may produce fibrillation, so 

 that in attempted resuscitation by cardiac massage care should be taken 

 not to apply this too vigorously. 



Auricles 



Although ventricular fibrillation is seldom recovered from, it has been 

 clearly shown in recent years that fibrillation of the auricles is relatively 

 common and that it is by no 'means immediately fatal. Indeed it is one 

 of the most common of the chronic cardiac disorders in man. Auricular 

 fibrillation can be produced experimentally by the- application of a 

 strong electric stimulus to the auricles. If, however, a weaker stimulus 

 is applied, the auricles do not go into typical fibrillation, but come to 

 beat at a very rapid and regular rate, perhaps three or four hundred a 

 minute. This condition is called " auricular flutter," and is quite fre- 

 quently observed in the clinic. 



The influence of auricular fibrillation and flutter on the beat of the ven- 

 tricle is an extremely important one in connection with the irregular- 

 ities of the heart observed in man, and this influence in most cases is 

 explained by considering (1) the narrowness of the path (in the auric- 

 uloventricular bundle) along which the impulses have to travel, and (2) 

 the varying conditions of excitability of the ventricular muscle, depend- 

 ing upon the existence of the refractory phase (page 180). 



In auricular flutter, when three or four hundred impulses per minute 

 are passing along the bundle to the ventricle, the contraction produced 

 by the first one will scarcely have started before the second and imme- 

 diately succeeding ones arrive, so that the ventricle will beat at a rate 

 that is much less than that of the auricle, and a condition simulating 

 heart-block will become established. The characteristic feature which 

 distinguishes this from true heart-block, however, is the fact that the 

 ventricular rate is above normal, whereas in true heart-block the rate 

 is much below normal. By means of the electrocardiogram or by 



