226 CIRCULATION. 



animal, warm or cold-blooded. This irritability, which is 

 manifested, under these circumstances, in precisely the same 

 way as in ordinary muscles, is different in degree in different 

 parts of the organ. Haller and others have shown that it is 

 greater in the cavities than on the surface ; for long after ir- 

 ritation applied to the exterior fails to excite contraction, the 

 organ will respond to a stimulus applied to its interior. The 

 experiments of Haller also show that fluids in the cavities of 

 the heart have a remarkable influence in exciting and keep- 

 ing up its contractions. This observation is of much interest, 

 as showing conclusively that the presence of blood is neces- 

 sary to the natural and regular action of the heart. We 

 quote one of the experiments on this point performed upon a 

 cat: 



a * * -x- ^ke superior vena cava having been divid- 

 ed, and the inferior ligated, and the pulmonary artery opened, 

 and the right ventricle emptied by a sufficient compression, 

 and the aorta ligated, all with promptitude, I saw the right 

 auricle repose first, the right ventricle continued to beat for 

 some time in unison with the left ventricle, and its walls de- 

 scended toward the middle line of the heart : but this ven- 

 tricle did not delay to lose its movement the first. As for 

 the other ventricle, which could no longer empty itself into 

 the aorta, it was filled with blood, and its movement contin- 

 ued for four hours. * * # 



This experiment was confirmed by numerous others. It 

 will be observed that one side of the heart was made to cease 

 its pulsations, while the other side continued to contract, by 

 simply removing the blood from its interior ; which conclu- 

 sively proves that, though the heart may act for a time in- 

 dependently, the presence of blood in its cavities is a stim- 

 ulus capable of prolonging its regular pulsations. Schiff has 

 gone still further, and succeeded in restoring the pulsations 

 in the heart of a frog, which had ceased after it had been 



1 HALLER, Memoir es sur la Nature Irritable et Sensible des Parties, etc., tome 

 i., p. 363. 



