264 THE CIRCULATION OF THE BLOOD 



Use the tracing obtained under the influence of Ringer's solution as a 

 normal and compare it with the rate and amplitude of the contractions 

 when the heart is perfused with: 



a. Physiological saline solution, then return to Ringer's solution; 



b. With saline and potassium chloride in the proportions found in 

 Ringer's solution (.7 per cent sodium chloride + .03 per cent potassium 

 chloride) ; 



c. With saline and calcium chloride in the proportions found in Ringer's 

 solution (.7 per cent sodium chloride + .026 per cent calcium chloride);, 



d. With Locke's solution; 



e. With milk diluted 4 volumes with physiological saline; 

 /. With normal serum, or blood; 



g. With blood, or serum, diluted four times with saline. 

 Tabulate the rates and amplitudes of the heart under these different 

 influences by the method previously followed. 



7. The Heart Volume. Isolate a frog's heart by the method de- 

 scribed for perfusing it with fluid in the preceding experiment. Connect 

 it in a Roy's tonometer, see figure 214, adjust the lever of the tonometer 

 for a tracing on smoked paper. This instrument records the change in 

 volume with each heart contraction. The influence of pressure, varied 

 between 2 and 10 cm., and of nutrient fluids on the heart volume may be 

 determined. 



An instructive demonstration can be had by placing the heart of the 

 cat or dog in a Henderson plethysmograph and recording the volume 

 changes by the tambour method. 



8. The Isolated Heart of the Terrapin. The heart of the terrapin, 

 being somewhat larger and somewhat more responsive than the heart of the 

 frog, may be substituted in the two immediately preceding experiments. 

 The facts obtained from it will be essentially the same as those obtained 

 from the frog's heart. 



9. The Isolated Mammalian Heart. The mammalian heart may be 

 isolated from the body and kept alive and contracting for many hours, 

 as has been demonstrated by numerous observers. It is only necessary 

 to keep the temperature approximately that of the normal body and to- 

 perfuse the heart through the coronary circulation with aerated blood, 

 or diluted blood, containing sufficient, aerated hemoglobin to supply the 

 heart with the requisite amount of oxygen. Or the heart may be kept 

 alive on the inorganic salt solutions, provided these are supplied with 

 oxygen under considerable tension (Porter, Howell). Even the human 

 heart has been isolated and kept contracting for some hours in the above 

 manner (Kuliabko). The method used is to insert a cannula into the 

 aorta and perfuse the heart through the coronary circulation under ade- 

 quate pressure, as described by Martin. Many interesting experiments 



