58 CIRCULATION OF THE BLOOD ACTION OF THE HEART. 



SUMMAEY OF CERTAIN CAUSES OF ARREST OF THE ACTION OF THE 



HEART. 



In warm-blooded animals, the heart's action speedily ceases after the organ 

 is deprived of its natural stimulus, the blood. Proof of this is not derived alone 

 from experiments on the inferior animals. It is well known that in profuse 

 haemorrhage in the human subject, the contractions of the heart are progress- 

 ively enfeebled, and when the loss of blood has proceeded to a certain extent, 

 are permanently arrested. Cases of transfusion after haemorrhage show that 

 when blood is introduced the heart may be made to resume its pulsations. 

 The same result takes place in death by asthenia ; and cases are on record 

 in which life has been prolonged, as in haemorrhage, 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 with 

 blood, continued to pulsate, showed that the absence of blood is competent 

 of itself to arrest contractions of the heart. The experiments of Erichsen, 

 who paralyzed the heart by tying the coronary arteries, and of Schiff, who 

 produced a local paralysis by tying the vessel going to the right ventricle, 

 show that the action of 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 haemorrhage. 



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 mechanical injury. A violent blow upon the deltoid 

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

 and in the same way, excessive distention of the cavities of the heart will 

 arrest its pulsations. This is shown by arrest of the circulation in asphyxia; 

 which is due to the fact that the heart is incapable of forcing the unaerated 

 blood through the systemic capillaries. The heart, in asphyxia, finally be- 

 comes enormously strained and distended and is consequently paralyzed. 

 The same result follows the application of a ligature to the aorta. This 

 effect may be produced 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 was performed upon the heart of 

 a large alligator : 



The animal was poisoned with curare, and twenty-eight hours after death 

 the heart, which had been exposed and left in situ, was pulsating regularly. 

 It was then removed from the body, and after some experiments on the com- 

 parative force, etc., of the pulsations when empty and when filled with blood, 

 was filled with water, the valves having been destroyed so as to allow free 

 passage of the fluid through the cavities, and the vessels were tied. The 

 ventricles, still filled with water confined in their cavity, were then firmly 

 compressed with the hand. From that time, the heart entirely ceased its 

 contractions and became hard like a muscle in a state of cadaveric rigidity. 



