300 ANALYSIS OF HEART BEAT. [BOOK i. 



one, two or several beats, and then comes to rest. In the majority 

 of cases, however, the animal having previously been in a vigorous 

 condition, it will after a while recommence its spontaneous beating, 

 the systole of the ventricle following that of the auricles ; but the 

 rhythm of beat will not be the same as that of the sinus venosus 

 left in the body, it will be slower, and the beats will not 

 continue to go on for so long a time as will those of a heart still 

 retaining the sinus venosus. 



When the incision is carried through the auriculo- ventricular 

 groove, so as to leave the auricles and sinus venosus within the 

 body, and to isolate the ventricle only, the results are similar but 

 more marked. The sinus and auricles beat regularly and vigor- 

 ously, with their proper sequence, but the ventricle, after a few 

 rapid contractions due to the incision acting as a stimulus, generally 

 remains for a long time quiescent. When stimulated however the 

 ventricle will give one, two or several beats, and after a while, in 

 many cases at least, will eventually set up a spontaneous pulsation 

 with an independent rhythm ; and this may last for some consider- 

 able time, but the beats are not so regular and will not go on for 

 so long a time as will those of a ventricle to which the auricles are 

 still attached. 



If a transverse incision be carried through the ventricle at 

 about its upper third, leaving the base of the ventricle still 

 attached to the auricles, the portion of the heart left in the body 

 will go on pulsating regularly, with the ordinary sequence of 

 sinus, auricles, ventricle, but the isolated lower two-thirds of the 

 ventricle will not beat spontaneously at all however long it be 

 left. Moreover in response to a single stimulus such as an in- 

 duction shock or a gentle prick it gives, not as in the case of the 

 entire ventricle when stimulated at the base or of the ventricle to 

 which the auricles are attached, a series of beats, but a single beat. 



Lastly, to complete the story, we may add that when the heart 

 is bisected longitudinally, each half continues to beat spon- 

 taneously, with an independent rhythm, so that the beats of the 

 two halves are not necessarily synchronous ; arid this continuance 

 of spontaneous pulsations after longitudinal bisection may be seen 

 in the conjoined .auricles and ventricle, or in the isolated auricles, 

 or in the isolated ventricle. Moreover the sinus or the auricles 

 may be divided in many ways and yet many of the segments 

 will continue beating ; small pieces even may be seen under 

 the microscope pulsating, feebly it is true but distinctly and 

 rhythmically. 



In these experiments then the various parts of the frog's heart 

 also form, as regards the power of spontaneous pulsation, a descend- 

 ing series : sinus venosus, auricles, entire ventricle, lower portion 

 of ventricle, the last exhibiting under ordinary circumstances no 

 spontaneous pulsations at all. 



155. Now we have seen ( 153) that these parts form 



