86 EXPERIMENTAL PHYSIOLOGY. 



the abdomen and is quickly dissected to both sides sufficiently to 

 expose the rib cartilages. The latter are then separately snipped 

 through on both sides by a bone forceps and finally the soft tissues 

 are cut through by a stout scalpel from below up. Arterial haemorr- 

 hage must be controlled by catching the bleeding points with a 

 haemostat and tying, but venous oozing can be stopped by applying 

 cloths wrung out with hot water. 



Watch the heart while the vagus nerve is being stimulated. 

 Place stout ligatures under the superior and inferior venae cavae 

 and tighten them for a few moments; note the emptying of the 

 heart. Place a ligature under the pulmonary artery and tighten 

 for a moment. Note the effect on the heart. Repeat with the 

 aorta. 



Listen to the sounds of the heart with a stethoscope applied 

 directly to various parts of it and study the effect produced on 

 the sounds by tightening the ligatures referred to above. Stop 

 the artificial respiration for a few moments and note the behaviour 

 of the heart. 



Afterwards excise the heart and open the right ventricle to 

 observe the contractions of the papillary muscles. Note that the 

 first sound is still heard in the excised heart. What conclusion do 

 you draw from this observation? 



