104 EXPERIMENTAL PHYSIOLOGY 



rhythmically when completely isolated from all other parts of the 

 heart ; (iv.) an isolated heart apex can more readily be made to beat 

 rhythmically if it be subjected to an internal pressure, as by tying it 

 on to a perfusion cannula through which fluid is circulated at sufficient 

 pressure. 



B. Taking it as proven that the rhythm is a property of the 

 muscle cells, it follows that the cells in different parts do not possess 

 the rhythmic capacity to an equal degree. The sinus, if left intact in the 

 body, beats with the same rhythm as the intact heart, and this, taken 

 in conjunction with the fact that the contraction wave starts normally 

 from the sinus, shows that in the sinus rhythmic activity is especially 

 developed. That the auricles and ventricle, when severed from the 

 sinus, beat at a slower rate is generally taken as indicating that the 

 auricles, the part from which the contraction wave starts when the 

 auricles and ventricle are removed, possess rhythmic characters to a 

 lesser degree than the sinus. Finally in the ventricle rhythmic activity 

 is still less developed, and with the ventricle apex can only be demon- 

 strated under especial conditions. 



Experiment 2. — The first Stannius ligature. Pith a frog and expose 

 its heart, cutting away the pericardium, so as to thoroughly expose the auricles 

 and two aortse. With an aneurism needle pass a thread tuider the bulbus 

 arteriosus and above the two superior cavae. Lift up the apex of the heart, cut 

 through the frenum, and bring the ends of the thread round the heart, so that 

 it lies under the auricles. Tie a loop in the thread and tighten it, so that it 

 lies over the crescentic junction of sinus and auricles after the ligature is 

 tightened. The auricles and ventricle usually give a few beats and then come 

 to rest in a fully relaxed condition, whilst the sinus continues to beat at the 

 same rate as before. At times the auricles and ventricle still continue 

 beating, though at a slower rate. This is usually due to the ligature being 

 wrongly applied. It should be relaxed and tied a second time a little nearer 

 to the auricle, when the required standstill will usually occur. 



In fig. 85 the effect of the application of the Stannius ligature is 



Fig. 85. — Application of the First Stannius Ligature to the Frog's Heart 

 at the Point a. At b a Beat due to a Mechanical Stimulus. 



recorded graphically. At the point a the ligature previously placed 

 in position was suddenly tightened. The two peaks immediately 



