212 EXPERIMENTAL PHYSIOLOGY. 



LESSON XLV. 



GRAPHIC RECORD OF THE FROG'S 

 HEART EFFECT OF TEMPERATURE. 



1. Graphic Record of the Contracting Frog's Heart. 



(a.) Pith a frog, or destroy its brain, and then curarise it. 

 Expose the heart, still within its pericardium, and arrange 

 a heart-lever, so that it rests lightly on the pericardium 

 over the beating heart. Adjust the lever to write on a 

 revolving cylinder, moving at a suitable rate (5-6 cm. per 

 second). Take a tracing of the beating of the heart. 



(b.) A suitable heart-lever is easily made with a straw about 

 12 inches long, or a thin strip of wood about the same length. 

 Thrust a needle transversely either through the straw or 

 wood, or through a piece of cork slipped over the straw 

 about 2 inches from one end of the lever. The needle 

 forms the fulcrum of the lever, and works in bearings, whose 

 height can be adjusted. To the end of the lever nearest 

 this is attached at right angles a needle with a small piece 

 of cork on its free end. The lever is so adjusted that the 

 cork on the needle rests on the heart. The long arm of the 

 lever is provided with a writing-style of copperfoil, or a 

 writing point made of parchment paper, fixed to it with 

 sealing-wax. By using a long lever a sufficient excursion 

 is obtained. 



(c.) Open the pericardium, expose the heart, and adjust 

 the cork on the lever. To obtain a good tracing, it is well 

 to put some resistant body behind the heart. Raise up the 

 ventricle, ligature the frsenum, and divide the latter outside 

 the ligature, and behind the heart place a pad of blotting- 

 paper moistened with normal saline, or a thin cover slip. 

 Adjust the lever, with its cork pad, on the junction of the 

 auricles and ventricle, to write on the cylinder, moving at 

 a slow rate (5-6 cm. per second), and take a tracing, noting 

 the rise and fall of the lever. 



