THE HEART BEAT. 513 



musculature, and although anastomoses may exist they appear 

 to be too incomplete to allow a collateral circulation to be estab- 

 lished when one of the main arteries is occluded. The portion of 

 the heart supplied by it dies, or to use the pathological term, under- 

 goes necrosis. On account of the pathological interests involved 

 the known serious results that may follow occlusion of any of the coro- 

 nary vessels or even any interference with the normal structure of the 

 vessels a number of investigations have been made upon animals 

 to determine the effect of occluding one or more of the coronary 

 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. 



Fibrillar Contractions. The arrest of the ventricles in the 

 experiments just described followed immediately or within a short 

 period, and the ventricles went into fibrillar 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, but the musculature in this part of 

 the heart seems to be able to return to its normal co-ordinated 

 contractions with much less difficulty. The cause of the sudden 

 change from co-ordinated to fibrillar contractions has never been 

 satisfactorily explained. In this connection it is interesting to 

 recall also that when any injury is done to either ventricle suf- 

 ficient to stop the contractions or cause fibrillation both ventricles 

 stop together. This result is doubtless due to the fact that their 

 musculature is, after all, one set of fibers common to both chambers. 



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

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

 1896. 



