298 TEXT-BOOK OF PHYSIOLOGY 



to rest and then perfusing it with Ringer's solution. As to whether 

 fibrillary contraction of the ventricle occurs in the human heart in conse- 

 quence of some pathologic occlusion of the coronary arteries there are no 

 methods of determining for death would promptly supervene as the result 

 of the cessation of the circulation of the blood which would follow loss 

 of coordinate systolic contraction. 



Auricular fibrillation, however, frequently occurs as a result, or con- 

 comitant of certain pathologic changes such as stenosis of the mitral 

 orifice. Owing to the increased resistance to the discharge of blood the 

 auricle becomes distended; possibly in consequence of a dissociation 

 of the fibers and an impairment in the conductivity, possibly in conse- 

 quence of an alteration in the irritability, fibrillation and incoordinate 

 contractions soon arise. Though originating in the left auricle, the 

 right auricle, either directly or indirectly, soon becomes involved. The 

 auricles, lacking coordinate systolic power cease to act as feed pumps 

 thus delaying the completion of the ventricular filling. Possibly in 

 consequence of the fibrillar contractions, excitatory impulses from regions 

 in association with the caval ends of the auriculo-ventricular bundle are 

 transmitted to the ventricle in an irregular manner and call forth frequent 

 and irregular contractions of the ventricles. Though the fibrillation of 

 the auricles is not immediately fatal, nevertheless the profound disturbance 

 of the circulation that arises, the fall of blood pressure and congestions 

 of viscera eventually leads to the death of the patient. 



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 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 308.) 



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 



