THE HEART BEAT. 559 



phenomenon, and disappears with the entrance of the first portion 

 of the blood from the auricles. While it may be of value in ac- 

 celerating the opening of the auriculoventricular valves, its influ- 

 ence does not extend to an actual suction of the blood from the 

 veins toward the heart. Other authors, however, on theoretical 

 grounds attribute more actual importance to the negative pressure 

 as a factor in moving the blood. 



Occlusion of the Coronary Vessels. — The coronary vessels sup- 

 ply the tissues of the heart with nutrition, including oxygen, so 

 that if the circulation is interrupted the normal contractions soon 

 cease. The branches of the large coronaries form what are known 

 as terminal arteries, — that is, each supplies a separate region of the 

 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 

 coronary vessels or even any interference with the normal structure 

 of the vessels — a number of investigations have been made upon ani- 

 mals 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. 



Fibrillation.— 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 tlie various fibers of tne ventricular muscle, m- 

 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 



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

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

 1896. 



