ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



61 



by drawing pins. A needle passes through the straw lever and holes 

 in the lead. A lump of modelling wax is placed on the long straw lever 

 as a counterpoise, and another piece of modelling wax attached to the 

 straw is arranged to rest on the heart. 



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 



FIG. 59. Method of recording the excised heart. 



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 



FIG. 60. Contraction of the frog's heart recorded by the suspension method 15 C. 

 and then immersed in saline at 25 C. The curve should be read from left to right 

 The time is marked in seconds. (L.H.) 



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 

 was attached to the ventricle is fastened to the lever. An elastic thread 

 is used as a spring as in Fig. 55 and the record taken by the suspension 

 method. Take a tracing of the heart when immersed in a beaker of 

 Ringer's fluid at room temperature (12-15 C.). Ringer's solution is 

 made by saturating O65 % 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 fluid which has been kept" in broken ice, and 

 take another record. The cooled heart gives slow and forcible beats. 



