INFLUENCE OF DIFFERENT NUTRIENT 1 FLUIDS 229 



move it completely from the body by first cutting the arteries at their branch- 

 ing in front of the bulbus arteriosus, then carefully lifting up the parts of 

 the heart and cutting away the great veins where they enter the sinus. This 

 will remove the entire heart, including all its contractile parts. The frog's 

 heart when thus removed and still wet with its own blood will continue con- 

 tracting rhythmically and in its natural sequence for some hours. Place 

 such an isolated heart in a watch-glass and take a record of its contractions, 

 by the apparatus described in the preceding experiment. 



Set this watch-glass on the metal warming-box supplied, and arrange 

 for the circulation of water of different temperatures through the box. Vary 

 the temperature of the box, and therefore of the heart placed upon it, by 

 allowing water of o C., 10 C., 20 C., 30 C., 40 C. to flow through it. 

 Record the contractions of the heart at each of these temperatures on the 

 recording drum as described in experiment 3 above. The heart being ex- 

 posed will not take the same absolute temperature as the box, but the relative 

 temperature will be decreased or increased. Tabulate the rates at these 

 different temperatures by the plan previously described. 



5. The Influence of Different Nutrient Fluids on the Excised 

 Heart. Expose a frog's heart, as previously described, and insert a can- 

 nula into the ascending vena cava just where it enters the sinus. Ligate 

 the descending vena cava, introduce a cannula into one of the branches of 

 the aorta, and carefully separate the heart from the body without injuring its 

 cavities within the points of ligature. Or the ligatures may be laid and the 

 cannulae inserted without separating the heart from the body. Connect 

 the venous cannula with a Mariotte's bottle filled with physiological saline, 

 0.7 per cent sodium chloride. Adjust the constant level tube for a pressure 

 of 6 cm. of fluid and allow the saline to flow through the heart. The arterial 

 cannula should be connected with a short rubber tube the mouth of which 

 allows the fluid to flow into a beaker or glass tumbler. The outlet of the 

 arterial tube should be about 2 cm. above the level of the heart so that the heart 

 must work against a slight pressure. The heart will continue its contractions 

 in good sequence and with a fairly rapid rate. Record the contractions on 

 the smoked paper of the recording drum, together with a time tracing in 

 seconds, the drum traveling at the rate of about 2 to 5 mm. per second. 



Use the tracing obtained under the influence of physiological saline solution 

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

 when the heart is perfused with Ringer's solution; with Locke's solution; with 

 saline and potassium in the proportion found in Ringer's solution; with 

 saline and calcium in the proportion found in Ringer's solution; with milk 

 diluted 6 vols. with saline; with normal serum or blood; with blood or serum 

 diluted four times with saline. Tabulate the rates and amplitude of the 

 heart under these different influences by the method previously followed. 



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



