112 



EXPERIMENTAL PHYSIOLOGY 



CHAPTEE X 



THE ACTION OP HEAT AND COLD UPON THE FBOG's HEART 



THE EFFECT OF HEAT AND COLD UPON THE EXCISED 

 BLOODLESS HEART 



Experiment 1. — Pith a frog and expose its heart. Cut through the 

 frenuru and pass a bent hook through the apex of the ventricle. Cut away 

 the lower jaw and now remove the heart entirely with the pericardium, 

 cutting out with it the surrounding tissues pretty freely. Pin this on to a 

 cork base fixed to a metal bar made in the foUowing way (fig. 93). Select a 

 round flat cork and bore through it from the side, making a hole sufficiently 

 large to fit tightly on the short arm of a brass L-piece. Fix the cork to the 

 L-piece with a little sealing-wax. The pins should pass through the floor 

 of the pericardium, so as to fix the heart firmly to the cork. The heart can 



be fitted to the recording lever as in 

 the previous experiments (see fig. 83). 

 A small beaker is then filled with defibri- 

 nated ox-blood, diluted with four times its 

 volume of normal saline, or with Ringer's 

 solution, 1 which has previously been 

 cooled in a freezing mixture to about 0° C. 

 The writing point is brought to the sur- 

 face and a chronograph marking seconds 

 arranged to write immediately under 

 it. The drmn is set in motion, and after 

 a short length of tracing has been taken 

 the beaker of cooled fluid is raised so 

 as to immerse the heart. The character 

 of the tracing is at once altered, and after 

 about half a minute, when the record no 

 longer changes, the fluid is lowered 

 and the gradual change in the beat, as 

 the temperature returns to its original 

 height, is recorded. Take several tracings 

 in this way, raising the temperature of the fluid five degrees for each fresh 

 tracing. 



Tracings obtained in this way are reproduced in fig. 94. In the first 



the heart was suddenly immersed in diluted blood at 4° C. The following 



beat is seen to be of less height and considerably prolonged, the second 



one of greater height, and then the heart settled down to a slow 



rhythm of considerable force in which the contraction was sustained 



at its height for some time, and relaxation was considerably prolonged. 



1 Kinger's solution is made by saturating 0-65 per cent. NaCl solution with 

 calcium phosphate and then adding 2 c.c. of a 1 per cent, solution of potassium 

 chloride to each 100 c.c. 



