166 THE CIRCULATION OF THE BLOOD 



THE RELATIVE IMPORTANCE OP THE VARIOUS CONSTITUENTS 

 OF THE PERFUSION FLUID 



We can study the chemical conditions necessary for resuscitation 

 of the heartbeat by observing the beat of an artificially perfused heart 

 while solutions of different chemical composition are being perfused 

 through the coronary vessels. At the outset we are impressed with the 

 fact that for successful resuscitation the organic constituents of the 

 nutrient fluid are of trivial importance compared with the inorganic 

 constituents. With a solution containing the proper proportion of in- 

 organic salts, and of course an adequate supply of oxygen, the heart 

 of a rabbit, for example, may be made to continue beating for several 

 days. It is true that it will beat longer if some of the organic con- 

 stituents of the blood plasma, particularly carbohydrate, are present, 

 but on the inorganic constituents alone its ability to beat is truly 

 remarkable. 



Observations on Cold-Blooded Heart 



The earlier experiments for the investigation of the chemical condi- 

 tions necessary for the maintenance of the heartbeat were performed 

 on the heart of the frog or turtle. By perfusing either of these hearts 

 with physiological sodium-chloride solution, it was observed that though 

 the beat might continue for some time, yet it gradually grew feebler 

 and feebler, until at last it ceased altogether with the heart muscle 

 in a condition of extreme relaxation or diastole. If small proportions 

 of potassium and calcium salts (as chloride) were added to the sodium- 

 chloride solution, the beat was much better maintained. Sidney 

 Ringer proved that the optimum concentration to produce efficient and 

 prolonged contraction for the heart of the frog or terrapin is as follows: 

 potassium chloride, 0.03 per cent; calcium chloride, 0.025 per cent. 

 The effectiveness of the solution was also found to be increased by the 

 addition of 0.003 per cent of sodium bicarbonate. This acts as a buf- 

 fer substance (page 36), holding the hydrogen-ion concentration at a 

 constant level. More recent work has shown that the hydrogen-ion con- 

 centration of the perfusion solutions is of considerable importance in 

 determining the efficiency of the beat, but the optimum is not the same 

 for the hearts of different kinds of animal, and indeed it may differ 

 for different parts of the same heart. 



The question naturally arises as to the relative importance of each 

 of the above salts; or rather, we should say, cations, since the anion, 

 chlorine, is the same for all of them. The function of the sodium chlo- 

 ride in the solutions is twofold: (1) to endow the solution with the 



