CAUSE OF RHYTHMICAL CONTRACTIONS OF THE HEART 45 



becomes paralyzed, like any muscle after a severe strain. It is probable 

 that the impediment to the capillary circulation results from contraction 

 of the arterioles of supply, due to irritation produced by the excess of 

 carbon dioxide in the blood. 



Cause of the Rhythmical Contractions of the Heart. The heart in 

 its structure bears a close resemblance to the voluntary muscles ; but it 

 has a constant office to perform and seems to act without external 

 stimulation. Its action resembles, in this regard, the movements of 

 cilia. The movements of the heart are involuntary. Its pulsations 

 can be neither arrested, retarded nor accelerated directly by an effort 

 of the will, except, of course, when retarded by voluntary arrest of 

 respiration or accelerated by violent muscular exercise or other indirect 

 means. Its property of rhythmical contraction, however, seems to 

 depend on the circulation of blood in its substance. If the coronary 

 arteries are tied, the heart ceases to beat in about twenty-three minutes 

 (Erichsen). The regular and efficient contractions of the heart, also, 

 are promoted by the passage of blood through its cavities. Although 

 the heart removed from the body will continue to contract spontaneously 

 and rhythmically for a time, its contractions soon cease, at least in 

 warm-blooded animals ; but during intervals of rest, a contraction may 

 be excited by direct stimulation. The nature of the liquid passing 

 through the heart has an influence on the character of its contractions. 

 When blood passes through its cavities, the pulsations are regular and 

 powerful ; but if water is substituted, the beats become more frequent 

 and are not so vigorous (Flint, 1861). 



It is certain that the muscular tissue of the heart has an inherent 

 property of rhythmical contraction. Under normal conditions, this con- 

 traction seems to be propagated from the auricles to the ventricles ; but 

 it is also true that the contractions of the heart are regulated through 

 the nervous system. When the heart is divided transversely at about the 

 middle of the ventricles, the upper portion continues to pulsate, while 

 the lower portion does not. The lower portion, however, still possesses 

 contractility and will respond to direct stimulation. This is thought to 

 be due to sympathetic ganglia that exist in the upper part, but not in 

 the lower part of the ventricles. In the frog there are three sympathetic 

 ganglia situated near the auricles : one, the ganglion of Remak, is at the 

 point where the inferior vena cava opens into the right auricle ; another 

 is between the left auricle and the right ventricle ; another is between the 

 two auricles. In man there is a chain of ganglia between the auricles 

 and the ventricles. It is probable that these ganglia are important in 

 regulating the action of the heart. 



In view of the results of experiments on the cold-blooded animals 



