PREPARATION OF THE HEART. 



(b.) Rub up in a mortar 4 grammes of dried ox blood (this 

 can be purchased) with 60 cc. of normal saline. Allow it 

 to stand some time, add 40 cc. of water, and filter. 



(c.) Ringer's Fluid. Take 90 cc. of -6 per cent. NaCl 

 solution, saturate it with calcic phosphate, and add 10 cc. of 

 a 1 per cent, solution of potassic chloride. 



2. Preparation of the Heart. 



(a.) Pith a frog, expose its heart, ligature and divide the 

 fnenum behind the ligature. 



(b.) Take a two-wayed cannula (Fig. 103), attach india- 

 rubber tubing to each tube, and fill the tubes and cannuhe 

 with the fluid to be perfused. Pinch 

 the india-rubber tubes with fine bull- 

 dog forceps to prevent the escape of the 

 fluid. 



(c.) Tie a fine thread to the apex of 

 the ventricle. To this thread a writing- c 

 lever is to be attached. 



(d.) By means of the frsenum ligature 

 raise the heart, with a pair of fine 

 scissors make a cut into the sinus, and 

 through the opening introduce the 

 double cannula passed through a cork, 

 until its end is well within the ven- 

 tricle. Tie it in with a ligature, the 



ligature constricting the auricles above the auriculo- ventricu- 

 lar groove, thus making what is known as a " heart-prepara- 

 tion." Cut out the heart with its cannula. 



(e.) In a filter-stand arrange a glass funnel, with an india- 

 rubber tube attached, at a convenient height, fill it with 

 the perfusion fluid, clamp the tube. Attach this tube to 

 one of the tubes -the inflow connected with one stem of 

 the cannula, taking care that no air-bubbles enter the tube. 

 Adjust the height of the reservoir so that the fluid can flow 

 freely through the heart, and pass out by the other tube of 

 the cannula. Place a vessel to receive the outflow fluid. 

 After a short time the heart will begin to beat. 



Fig. 103. Cannula 

 for Frog's Heart. 



