CHAPTER IX. 



Involuntary muscle. Cut a transverse strip 

 from the stomach of a recently fed frog, and attach 

 to a light muscle lever in exactly the same way as 

 with a voluntary muscle. Keep moist with Ringer's 

 solution. Allow the lever to write upon a very 

 slowly revolving drum. Place a pair of stimulating 

 electrodes in contact with the fixed end of the strip, 

 and excite by allowing the drum to make and break 

 a galvanic circuit. Record the resulting contraction 

 and determine its period of latency. 



The strip will probably be found to contract 

 spontaneously and rhythmically after a time. Re- 

 cord these contractions. 



The frog-heart. Examine the contracting 

 heart of a pithed frog, cutting away the sternum 

 and ensiform cartilage and the front of the peri- 

 cardium. Gently raise the tip of the ventricle with 

 a blunt hook, and tie a thread to the pericardial liga- 

 ment which binds the ventricle to the back of the 

 pericardium. Cut the ligament beyond the thread 

 and raise the heart by the latter. Do not grasp 

 the heart with forceps. 



Notice the sinus venosus receiving the two venae 

 cavae superiores and the vena cava inferior; the 

 double auricle ; the single ventricle ; and on the 

 front the bulbus aortse leaving the ventricle and 



