RHYTHMICAL CONTRACTIONS OF THE HEART. 57 



It, is unnecessary to refer to the various experiments which have demonstrated the 

 in lepen deuce of the contractions of the heart. They are of such a simple nature that 

 they may be verified hy any one who will take the trouble to excise the heart of a frog 

 or turtle, place it under a small bell-glass so that it will not be subject to possible irrita- 

 tion from currents of air, and watch its pulsations. In such an observation as this, it is 

 evident that, for a certain time, contractions, more or less regular, will take place; and 

 the experiments referred to above show that they occur without any external influ- 

 ence. In short, it is evident that the muscular fibres of the heart possess an irritability, 

 by virtue of which they will contract intermittently for a time, although no stimulus be 

 applied ; as the ordinary striated muscular fibres have an irritability, by virtue of which 

 they will respond, for a time, to the application of a stimulus. 



It is manifestly necessary that the action of the heart should be constant, regular, and 

 powerful ; and when we say that the irritability inherent in its muscular tissue is such 

 that it will contract for a time without any external stimulus, we by no means assume 

 that this is the cause of its physiological action. It is only an important and incontestable 

 property of the muscular fibres of the heart, and its regular action is dependent upon 

 other conditions. 



In the first place, we have to inquire what makes the action of the heart regular. 

 The answer to this is, that the changes of nutrition, by which, through the blood circu- 

 lating in its substance, the waste of its tissue is constantly supplied, preserve the integrity 

 of the fibres, and keep them, consequently, in a condition to contract. This is true, 

 likewise, of the ordinary striated muscular fibres. If the supply of blood be cut off from 

 the substance of the heart, especially in the warm-blooded animals, the organ soon loses 

 its irritability. This was admirably shown by the experiments of Erichsen. This 

 observer, after exposing the heart in a warm-blooded animal and keeping up artificial 

 respiration, ligated the coronary arteries, thus cutting off the greatest part of the supply 

 of blood to the muscular fibres. He found, as the mean of six experiments, that the heart 

 ceased pulsating, although artificial respiration was continued, in 23 minutes. After the 

 pulsations had ceased, they could be restored by removing the ligatures and allowing the 

 blood to circulate again in the substance of the heart. 



In the second place, the regular and powerful contractions of the heart are provided 

 for by the circulation of the blood through its cavities. Although the heart, removed 

 from the body, will contract for a time without a stimulus, it can be made to contract 

 during the intervals of repose by an irritant, such as the point of a needle or a feeble 

 current of galvanism. For a certain time after the heart has ceased to contract sponta- 

 neously, contractions may be induced in this way. This can easily be demonstrated in 

 the heart of any animal, warm-blooded 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 irritation 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 keeping up its contractions. This observa- 

 tion is of much interest, as showing conclusively that the presence of blood is necessary 

 to the natural and regular action of the heart. We quote one of the experiments on this 

 point performed upon a cat : 



" . . . . The superior vena cava having been divided, and the inferior limited, 

 and the pulmonary artery opened, and the right ventricle emptied by a sufficient com- 

 pression, 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 ventri- 



tain franslla ; but this point cannot be regarded as definitively settled and is e\-oe<'.lin.<;Iy dilnYnlt to dftmnino. The 

 fact that nervous and muscular irritability are entirely distinct from each other is a strong argument in favor of tho 

 Independent irritability of tho inuscubr tissue of the heart. 



