9G DURATION OF THE MOVEMENTS OF THE HEART. 



55. Duration of the Movements of the Heart. 



That the heart continues to beat for some time after it is cut out 

 of the body, was known to Cleanthes, a contemporary of Herophilus, 

 300 B.C. The movement lasts longer in cold-blooded animals (frog, 

 turtle, fish) extending even to days than in mammals. A rabbit's heart 

 beats from 3 minutes up to 36 minutes after it is cut out of the body. 

 The average of many experiments is about 1 1 minutes. Panum found 

 the last trace of contraction to occur in the right auricle (rabbit) 

 15 hours after death ; in a mouse's heart, 46 hours; in a dog's, 96 hours. 

 An excised frog's heart beats, at the longest, 2| days (Valentin). In 

 a human embryo (third month) the heart was found beating after 

 4 hours. In this condition stimulation causes an increase and accelera- 

 tion of the action. Afterwards, the ventricular contraction first becomes 

 weaker, and soon each auricular contraction is not followed by a 

 ventricular contraction, two or more of the former being succeeded by 

 only one of the latter. At the same time the ventricles contract more 

 slowly (Fig. 27), and soon stop altogether, while the auricles still con- 

 tinue to beat. If the ventricles be stimulated directly, as by pricking 

 them with a pin, they may execute a contraction. The left auricle 

 soon ceases to beat, while the right auricle still continues to contract. 

 The right auricular appendage continues to beat longest, as was 

 observed by Galen and Cardan us (1550). The term " ultimum 

 moriens " is applied to it. Similar observations have been made upon 

 the hearts of persons who have been executed. 



If the heart has ceased to beat, it may be excited to contract for a 

 short time by direct stimulation (Harvey), more especially by heat ; 

 even under these circumstances, the auricles and their appendages are 

 the last parts to cease contracting. As a general rule, direct stimula- 

 tion, although it may cause the heart to act more vigorously for a 

 short time, brings it to rest sooner. In such cases, therefore, the 

 regular sequence of events ceases, and there is usually a twitching 

 movement of the muscular fibres of the heart. C. Ludwig found that 

 even after the excitability is extinguished in the mammalian heart, it 

 may be restored by injecting arterial blood into the coronary arteries: 

 lesion of these vessels is followed by enfeebled action of the heart 

 (p. 75). Hammer found that in a man, whose left coronary artery was 

 plugged, the pulse fell from 80 to 8 beats per minute. 



Action of Gases on the Heart. During its activity the heart uses 

 0, and produces CO.,, so that it beats longest in pure (12 hours) 

 (Castell), and not so long in N, H (1 hour) C0 2 (10 minutes), CO 

 (42 minutes) Cl (2 minutes), or in a vacuum (20 to 30 minutes) 

 (Boyle, 1670; Fontana, Tiedemann, 1847), even when there is watery 



