652 SPECIAL PHYSIOLOGY. 



beats only a few minutes after their execution ; this is also true of the 

 warm-blooded animals. Its contractions continue much longer, after 

 systemic death, in cold-blooded and hibernating creatures. The 

 actions of the heart become slower and irregular, ceasing last in the 

 right auricle, the so-called ultimum morirns. They are stimulated by 

 heat, the injection of fresh blood, the action of oxygen, and by gal- 

 vanism ; they are arrested by carbonic acid, sulphuretted hydrogen, the 

 vapor of chloroform, and also, after a time, in a complete vacuum. 



The beats of the heart, recurring at more or less regular intervals, 

 exhibit an example of so-called rhythmic action ; their rhythm, like 

 that of the respiratory movements, is, indeed, very remarkable. The 

 cause of this rhythm was, at one time, supposed to be the stimulation 

 of the inner surface of the cavities of the heart by the blood, and it 

 was further imagined that some relation might exist between the 

 special irritability of the right side of the heart, and the qualities of 

 the dark or venous blood returning from the body, and also between 

 that of the left side of the heart, and the qualities of the red or ar- 

 terial blood entering them from the lungs. Moreover, the ventricles, 

 stimulated to contract by their contents, were supposed, after forcing 

 the blood through the body and lungs respectively, to accomplish the 

 filling of the auricles ; the contraction of these, excited in a similar 

 manner by their contents, was supposed once more to fill the ventri- 

 cles, and so on. The muscular walls of the heart undoubtedly possess 

 great irritability even in a warm-blooded animal ; the inner surface of 

 the auricles and ventricles is also both sensitive and excitable, and is 

 certainly more rapidly acted on by poisons than their outer surface. 

 (Henry.) But the heart, or even a separate portion of that organ, 

 taken from a hibernating warm-blooded, or from any cold-blooded 

 Vertebrate animal, may not only retain its general irritability for 

 days, but may continue, for a time, to perform rhythmic contractions 

 and dilatations, even if removed from the body, though no blood is 

 left in it, and though freed from the stimulus of oxygen, as when 

 placed in a vacuum. The frog's heart will beat thus for twelve hours. 

 Although, therefore, the rhythmic motions of the heart in the living 

 animal may be partly due to the stimulus of the blood entering its 

 cavities, yet this cannot, under all circumstances, be the cause of such 

 rhythmic actions. 



Through the pneumogastric nerves, the cerebro-spinal nervous cen- 

 tres, as shown by experiment and by observation in disease, greatly 

 influence the heart's action, under some circumstances increasing, 

 and under others, lowering or inhibiting it (p. 307); but there is no 

 evidence of their being the cause of the rhythmic character of its 

 movements. The action of the heart is influenced by the emotions 

 and passions, and, according to some, even by the will. In the cele- 

 brated case of Colonel Townsend, recorded by Cheyne, the breath 

 could be held, and thus the movements of the heart could be controlled 

 by an act of the will. The heart is excited or depressed by various 

 diseases of the brain, as by cerebral inflammation on the one hand, 

 and by apoplexy on the other ; and its action is disturbed, or even 

 abruptly suspended, by severe injury or destruction of the brain or 



