THE CIRCULATION OF THE BLOOD 297 



previous experiments on rings of the coronary artery of the human heart 

 the conclusion is drawn, that in man and the monkey, epinephrin constricts 

 the coronary arteries even though it dilates them in the dog, cat, rabbit, 

 and other animals. From these result the further conclusion is drawn that 

 in man and monkeys the coronary arteries are supplied with vaso-constrictor 

 nerves of true sympathetic (thoracico-lumbar) origin. 



The Effects of Ligation of the Coronary Arteries. As stated in a 

 foregoing paragraph the nutrition of the heart-muscle, its irritability and 

 contractility, depend on the blood-supply derived from the coronary vessels. 

 This is shown by the effects which follow its withdrawal. Ligation of both 

 coronary arteries in the dog is followed by a diminution in the force and 

 frequency of the heart-beat, and in a few minutes by complete cessation. 

 Ligation of even a single branch of a coronary artery of the dog heart, pro- 

 vided it supply a sufficiently large territory e.g., the arteria circumflexa 

 is sufficient to cause arrest in at least 80 per cent, of animals (Porter). With 

 the ligation of this vessel there occurs a gradual diminution in the force and 

 frequency of the systole. As the power of coordinate contraction declines 

 the heart-muscle frequently exhibits a series of independent contractions of 

 individual fibers and cells known as fibrillary contraction. All the results 

 which follow ligation are to be attributed in the light of experiment to the 

 sudden anemia which is thus established. The removal of the ligature and 

 the return of the blood will restore the nutrition and re-establish coordinate 

 contractions. The excised heart of the mammal which has passed into the 

 condition of fibrillary contraction may be again made to beat rhythmically 

 and vigorously by first cooling it with normal saline, and then perfusing it 

 with warm defibrinated blood through the coronary vessels under a suitable 

 pressure. The same result can be brought about by first perfusing it with 

 a i per cent, solution of potassium chlorid until the heart comes to rest and 

 then perfusing it with Ringer's solution. 



The Beat of the Excised Heart. The beat of the heart, its frequency 

 and regularity, its continuance from the early stages of fetal development till 

 death, has long been an interesting subject for physiologic investigation. 

 Though related to the functional activities of the body at large, the activity 

 of the heart is in a sense independent of them, for it will continue for a 

 variable length of time after they have ceased. The heart of the frog or 

 the turtle will continue to beat under appropriate conditions for hours after 

 separation of all anatomic connections and removal -irojn the body. The 

 heart of the dog or cat will, however, beat but for a few minutes. The 

 human heart would in all probability act in the sameway. Nevertheless 

 there are good reasons for believing that though the heart has ceased to 

 respond to its customary stimulus, the irritability yet endures though 

 perhaps in lessened degree, by reason of the absence of blood, in the mam- 

 malian heart, in the coronary system of vessels. For if, after the heart has 

 ceased to beat for some time, warm defibrinated and oxygenated blood 

 or Locke's modification of Ringer's solution be passed through the coronary 

 vessels the beat will reappear and continue at its usual rate for some hours. 

 (See paragraph relating to the action of inorganic salts on the mammalian 

 heart, page 307.) 



The reason for the longer continuance of the beat of the excised hea: 

 of the cold-blooded animal beyond that of the warm-blooded animal 



