THE HEART BEAT. 563 



vessels.* It would seem from Porter's experiments that the results 

 of such an operation vary according to the size of the area deprived 

 of its blood. When the arteria septi alone was occluded the heart 

 was not affected, when the arteria coronaria dextra was occluded 

 the ventricular contractions were arrested in 18 per cent, of the 

 cases observed. Occlusion of the ramus descendens of the left 

 coronary artery caused arrest of the ventricles in 50 per cent, of the 

 cases, while occlusion of the circumflex branch of the same artery 

 caused arrest in 80 per cent, of the cases. Ligation of three of the 

 arteries caused stoppage of the heart in all cases. 



Fibrillary Contractions. The arrest of the ventricles in the 

 experiments just described followed immediately or within a short 

 period, and the ventricles went into fibrillary contractions. In this 

 curious condition the various fibers of the ventricular muscle, in- 

 stead of contracting together in a co-ordinated fashion, contract 

 separately and irregularly; so that the surface of the ventricle has 

 the appearance of a vibrating, twitching mass. Such a condition 

 in the ventricle is usually fatal that is, the musculature is not able 

 to recover its co-ordinated movement. This condition may come 

 on with great suddenness as the result of occlusion of the arteries, 

 of injury to certain parts of the heart, or from strong electrical 

 stimulation. Fibrillation of the auricles also occurs frequently 

 under experimental conditions, and, indeed, in the human heart ap- 

 parently under pathological conditions. When the auricles are 

 thrown into fibrillation by experimental means the ventricles con- 

 tinue to beat, but in an irregular manner similar to a condition 

 sometimes observed in man and described usually under the term 

 pulsus irregularis perpetuus. There is reason to believe that this 

 condition in man is attributable to a fibrillation of the auricles* | 

 The cause of the sudden change from co-ordinated to fibrillary con- 

 tractions has never been satisfactorily explained. It has been 

 suggested, on the one hand, that it is due to some alteration in the 

 normal process of conduction, the interposition of partial or com- 

 plete blocks in the course of the excitation wave, and, on the other, 

 that it is caused by the independent formation of impulses in 

 many foci throughout the cardiac musculature. 



* For a description of results and the literature see Porter, "Journal of 

 Physiology," 15, 121, 1893; also "Journal of Experimental Medicine," 1, 1, 

 1896. 



t Cushny, "American Journal of the Medical Sciences," June, 1911. 



