RHYTHM OF THE HEART. 131 



in the nervous ganglia of the heart, and in all parts 

 originating rhythmic processes, the same alternation of 

 periods of action with periods of repose, during which the 

 waste in the structure is repaired, as is observed in most 

 of, if not all, the organic phenomena of life. All organic 

 processes seem to be regulated with exact observance of 

 time ; and rhythmic nutrition and action, as exhibited in 

 the action of the heart, are but well-marked examples of 

 such chronometric arrangement. 



We may conclude, then, that the nervous ganglia in 

 the heart's substance are the immediate regulators of the 

 heart's action, but that they are themselves liable to in- 

 fluences, conveyed from without, through branches of the 

 pneumogastric and sympathetic nerves. 



The pneumogastric nerves are the media of an inhibitor)/ 

 or restraining influence over the action of the heart ; for 

 when by section their influence is withdrawn, the pulsa- 

 tions of the organ are increased in frequency and strength ; 

 while an opposite effect is produced by stimulating them, 

 the transmission of an electric current of even moderate 

 strength, diminishing the pulsations, or stopping them 

 altogether. Stimulation of the sympathetic nerves, on the 

 other hand, accelerates and strengthens the heart's action. 



Various theories have been proposed to account for 

 these peculiar results, but none of them are very satis- 

 factory, and it is probable that many more facts must be 

 discovered before any theory on the subject can be per- 

 manently maintained. 



The connection of the action of the heart with the other 

 organs, and the influences to which it is subject through 

 them, are explicable from the connection of its nervous 

 system with the other ganglia of the sympathetic, and with 

 the brain and spinal cord through, chiefly, the pneumo- 

 gastric nerves. But this influence is proved in a much 

 more striking manner by the phenomena of disease than 

 by any experimental or. other physiological observations. 



