132 THE CIRCULATION. 



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 

 established by the results of several experiments, of which 

 the following is one of the most conclusive: Dr. Sharpey 

 injected bullock's blood into the thoracic aorta of a dog 

 recently killed, after tying the abdominal aorta above the 

 renal arteries, and found that, with a force just equal to 

 that by which the ventricle commonly impels the blood in 

 the dog, the blood which he injected into the aorta passed 

 in a free stream out of the trunk of the vena cava inferior. 

 It thus traversed both the systemic and hepatic capillaries ; 

 and when the aorta was not tied above the renals, blood 

 injected under the same pressure flowed freely through the 

 vessels of the lower extremities. A pressure equal to that 

 of one and a half or two inches of mercury was, in the 

 same way, found sufficient to propel blood through the 

 vessels of the lungs. 



But although it is probably true that the heart's action 

 alone is sufficient to ensure the circulation, yet there exist 

 several other forces which are, as it were, supplementary 

 to the action of the heart, and assist it in maintaining the 

 circulation. The principal of these supplemental forces 

 have been already alluded to, and will now be more fully 

 pointed out. 



