G6 



EXPERIMENTAL PHYSIOLOGY 



Using a watch, count the number of beats per minute during 

 several minutes and record the result. 



Effect of heat and cold on rate of beat. Now apply, first, an ice- 

 cold and, second, a warmed thick wire (a) to the ventricle, (6) to one 

 of the auricles, (c) by turning up the heart, to the sinus. Count the 

 rate during each application, and record the results. 



Out edge of septum. 



Auricular septum. 



Left auricle. 



Aur.-ventr. valve. 



Eight auricle. 



Ventricle. 



FIG. 58. SECTION THKOUGH HEART OP FROG. FRONT HALF SEEN FROM BEHIND 

 (GAUPP). ?. THE SPONGY STRUCTURE OP THE VENTRICLE is WELL SHOWN. 



Stannius' experiment. Raise the ventricle very carefully without 

 pinching or injuring it in any way, and, after cutting a ligament or 

 fold of pericardium which encloses a small vein, pass a thread under 

 the sinus, and tighten it round the sino-auricular junction, which is 

 marked by a whitish line. The sinus continues to beat as before 

 (count the rate), but the auricle and ventricle come to a standstill 

 in diastole. Such a heart is termed a Stannius heart. 



Septum of auricles. 



Orifice of pulmonary vein. 



Left vagus nerve. 

 - Bidder's ganglion. 



Right vagus nerve. - 



Ventricle. 



FIG. 59. HEART OF FROG WITH LEFT AURICLE cur OPEN TO SHOW THE VAGUS 

 NERVES IN THE AURICULAR SEPTUM (GAUPP). j. 



Stimulate auricle or ventricle, and notice that each stimulation is 

 followed by a contraction. They are therefore not inhibited, but 

 have ceased to contract owing to their being cut off by the ligature 

 from the sinus (in which the contractions normally begin). 



Now tie a second ligature round the auriculo- ventricular junction. 

 The ventricle usually gives a few (three or four) beats, and then both 



