THE PROPERTIES OF THE HEART MUSCLE IQ7 



ence with its rhythmical contractions. Further, in an animal rapidly bled 

 to death, the heart continues to beat for a time, varying in duration with 

 the kind of animal experimentally dealt with 



* 



and depending on whether or not there is entire 



absence of blood within the heart chambers. 



Furthermore, if the heart of an animal be removed , .S 



from the body, it still continue its alternate sys- 



tolic and diastolic movements for a varying time. 



Thus we see the power of rhythmic contraction 



depends neither upon connection with the central 



nervous system nor yet upon the stimulation 



produced by the presence of blood within its 



chambers. Whether or not rhythmicity is a prop- 



erty of heart muscle, as such, was conclusively 



settled by Gaskell and by numerous later investi- ~ 



gators by a very simple experimental procedure. 



Gaskell cut thin strips of the apex of the ventricle ^^^^HH| 

 of the terrapin, which is free from the nerve cells, 

 at least nerve ganglia, and found that they con- ^1 

 tracted rhythmically for hours. This experiment 



has become a classic one for the study of the .2 



cardiac muscular tissue. Strips of cardiac mus- 

 cle cut from the auricle and from the contractile H 

 walls of the venae cavae, or sinus venosus, of the ' 

 terrapin also contract rhythmically. If the strips 

 of muscle are kept moist with the same blood ^^^^_ , 

 or serum, then the rhythm of the sinus is greater j~ if I 

 than that of the auricle, and that of the auricle g ;| ' 

 greater than that of the ventricle, a difference , .S 

 that is based on a physiological differentiation 

 of the tissue. The sinus muscle is also more _^_^^^^^^_ 

 delicately responsive to stimuli than is the ven- M *o - 

 tricular muscle; i.e., it is more irritable. - 



Porter first performed the more difficult ex- ^^^^^^^mm #-& 

 periment of isolating a small disc of muscle from 



the ventricle of the dog, leaving only the delicate - . , J "Sis 



nutrient artery through which the muscle was 

 fed with defibrinated blood. This isolated small \ j| ,\ 



piece of ventricle contracted vigorously for many t 



minutes. Moorhouse has recently shown that 



various portions of the auricle, the sinus, and .; .r S ^ 



the veins contract in good rhythm. They also ,,;--; 



respond to various drugs in a characteristic HHHEBHU 



