CAUSES OF ARREST OF THE ACTION OF THE HEART. 237 



heart are progressively enfeebled, and, when the loss of blood 

 has proceeded to a certain extent, are permanently arrested. 

 Cases of transfusion after hemorrhage show that when blood 

 is introduced, the heart may be made to resume its pulsa- 

 tions. The same result takes place in death by asthenia ; and 

 cases are on record where life has been prolonged, as in hem- 

 orrhage, by transfusion of even a small quantity of healthy 

 blood. These facts have been demonstrated on the inferior 

 animals by experiments already cited. The experiment of 

 Haller, in which the action of the right side of the heart of a 

 cat was arrested by emptying it of blood, while the left side, 

 which was filled w T ith blood, continued to pulsate, showed 

 that the absence of blood in its cavities is competent of itself 

 to arrest the heart. The experiments of Erichsen, who par- 

 alyzed the heart by ligating the coronary arteries, and Schiff, 

 who produced a local paralysis by ligating the vessel going to 

 the right ventricle, show that the heart may also be arrested 

 by cutting off the circulation of blood in its substance. Both 

 of these causes must operate in arrest of the heart's action 

 in hemorrhage. 



The mechanical causes of arrest of the heart's action are 

 of considerable pathological importance. The heart, in 

 common with other muscles, may be paralyzed by sufficient 

 mechanical injury. A violent blow upon the deltoid paralyzes 

 the arm ; a severe strain will paralyze the muscles of an 

 extremity ; in the same way excessive distention of the cav- 

 ities of the heart will arrest its pulsations. This is shown by 

 arrest of the circulation in asphyxia. We have already seen, 

 that under these circumstances the heart is incapable of 

 forcing the unaerated blood through the systemic capillaries ; 

 it finally becomes enormously strained and distended, and 

 consequently paralyzed. The same result follows the appli- 

 cation of a ligature to the aorta. This effect may be pro- 

 duced, also, in the cold-blooded animals, in which, if the 

 heart be left undisturbed, the pulsations will continue for a 

 long time. The following experiment illustrating this point 



