64 



PRACTICAL PHYSIOLOGY 



II. The Initiation of Contraction 

 What is the Influence of the Sinus? Stannius Experiment 



By means of a needle, pass a piece of thread under the two aortae, 

 and, turning the ventricle forward, tie a loose loop between the 

 auricles and the sinus (Figs. 61 to 64). When the heart has 

 recorded a few contractions, swing the point of the lever off the 

 drum, tie the loop tightly so as to separate the auricles from the 



FIG. 61. 



FIG. 62 



FIG. 63 (side view). 



1. Ventricle. 



2. Auricle. 

 4. Sinus. 



5. Aorta. 



7. Inferior Vena Cava. 



... 3 



FIG. 64. Stannius heart. The first 

 and second ligatures (Hedon). 

 1, Auricle ; 2, Sinus ; 3, Ventricle. 



sinus, swing the point of the lever on and record the results. Has 

 the sinus any important influence in initiating contraction ? 



Swing the lever off again and tie another loose loop round the 

 auriculo- ventricular groove, and tighten it so that it exactly separates 

 the auricles from the ventricle. Record the result and formulate 

 your conclusion as to other parts of the heart besides the sinus 

 having the property of initiating contraction (Fig. 65). 



