THE CIRCULATION OF THE BLOOD. 289 



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 from 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 same way. Nevertheless 

 there are good reasons for believing that though the spontaneous beat has 

 ceased, the irritability yet endures though perhaps in lessened degree. 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 299.) 



The reason for the longer continuance of the beat of the excised heart 

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

 lies probably in the difference in the rate of their respective metabolisms. 

 There is reason to believe that each cell of the heart-muscle, in common with 

 other tissue-cells, during life stores up and holds in reserve a larger quantity 

 of nutritive material than is necessary for its immediate needs. When sepa- 

 rated from the general blood-supply, the cells begin to utilize this reserved 

 material. With its consumption the irritability declines and after a variable 

 period of time the contraction ceases. As the metabolism is far more rapid 

 in the warm-blooded than in the cold-blooded animal, it is probable that the 

 reserved nutritive material is utilized more quickly in the former than in the 

 latter other conditions being equal. So long as it lasts in either class, the 

 irritability and contractility persist. 



Whatever the immediate or exciting cause of the heart contraction may be, 

 the fundamental condition for its manifestation is the maintenance of the 

 irritability. So long as this persists at a sufficiently high level the heart- 

 muscle will contract in response to the appropriate stimulus. 



THE PHYSIOLOGIC PROPERTIES OF THE HEART-MUSCLE. 



The physiologic properties of the heart-muscle on which its efficiency as 

 a pumping organ depends, viz., irritability, conductivity, rhythmicity, 

 tonicity, automaticity, have been largely determined by a study of the heart 

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