142 THE CIRCULATION. 



fluences conveyed from without, through, branches of the 

 pneumogastric and sympathetic nerves. 



It is generally believed that the pneumogastric nerves 

 are the media of an inhibitory influence over the action of 

 the heart, from the fact that when by section their influence 

 is withdrawn, the pulsations of the organ are increased in 

 frequency and strength ; and, again, that 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. 

 The influence of a shock in arresting or modifying the 

 action of the heart, its very slow action after compression 

 of the brain, or injury to the cervical portion of the spinal 

 cord, its irregularities and palpitations in dyspepsia 

 and hysteria, are better evidence for the connection of 

 the heart with the other organs through the nervous 

 system, than are any results obtained by experiments. 



Effects of the Heart's Action. 



That the contractions of the heart supply alone a suffi- 

 cient force for the circulation of the blood, appears to be 



