2 SO PRACTICAL PHYSIOLOGY. [LVIII. 



the blood is thoroughly shaken up with air before mixing it. This 

 is the best fluid to use. 



(6.) Ringer's Fluid. Take 99 cc. of .6 per cent. NaCl solution, 

 saturate it with calcic phosphate, and add I cc. of a i per cent, 

 solution of potassic chloride. 



(c.) Rub up in a mortar 4 grams 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. 



2. Preparation of the Heart. 



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

 behind the ligature. 



(/;.) Take a two-way ed cannula (fig. 202), attach india-rubber 

 tubing to each tube, and fill the tubes and cannulae with the 

 fluid to be perfused. Pinch the india-rubber 

 tubes with fine bull dog forceps to prevent the 

 escape of the fluid. 



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

 ventricle. To this thread a writing-lever is to 

 be attached. 



(d.) By means of the frsenum ligature raise 

 the heart, with a pair of scissors make a cut 

 into the sinus, and through the opening intro- 

 duce the double cannula passed through a 

 cork, until its end is well within the ventricle. 

 Tie it in with a ligature, the ligature constrict- 

 ing the auricles above the auriculo-ventricular 

 FIG. 202. Kronecker's groove, thus making what is known as a 

 cannula for Frog's hear t-preparation." C ut 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 (6-7 inches above the heart), 

 fill it Avith 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. 



(/".) Place the heart in a cylindrical glass tube, fixed on a stand, 

 and arranged so that the cork in which the cannula is fixed fits 

 into the mouth of the tube. A short test-tube does perfectly 

 well. The lower end of the glass tube has a small aperture in it 

 through which the thread (c) is passed, and attached to a writing- 

 lever arranged on the same stand as the glass vessel. See that 



