ELEMENTAEY EXPEEIMENTAL PHYSIOLOGY 



99 



drum (slow rate). Note the auricular and ventricular curves, and the 

 rounded top or plateau 

 of the ventricular curve. 

 Kender the heart blood- 

 less by opening an 

 auricle. The apex of the 

 ventricular curve becomes 

 pointed. Internal ten- 

 sion excites the muscle 

 of the heart to more 

 prolonged and sustained 

 contractions. 



Another method of re- 

 cording the heart is shown 

 in Fig 93. A long light 

 straw lever is taken, and 

 a needle is passed through 

 it. The needle plays in 

 holes in the brass upright, 

 as shown. 



Effect of Heat and Cold on the Excised Frog-heart. Expose the 

 heart of a pithed frog. Pass a small hook attached to a thread through 

 the tip of the ventricle. Excise the whole heart, cutting widely round 

 it, and pin the tissues surrounding the base of the heart to a cork 

 which is attached to the bottom of the vertical limb of a T-piece. 

 The T-piece is placed beneath the recording lever, and the thread which 



Fio. 93. Lever, for recording the frog's heart. 

 (Perabrey and Phillips.) 



The thread from the heart is attached 



Fio. 94. Heart chamber. 



was attached to the ventricle is fastened to the lever (Fig. 94). Take 

 a tracing of the heart when immersed in a beaker of E-inger's fluid at 

 room temperature (12-15 C.). Kinger's solution is made by saturating 

 0-65 % NaCl with calcium phosphate and adding to each 100 c.c. of 

 this solution 2 c.c. of 1 % KC1. Next fill the beaker with Ringer's 



