252 THE CIRCULATION OF THE BLOOD 



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. Or 

 place the heart in a watch-glass over a drinking glass of water of the proper 

 temperature. Record the contractions of the heart at each of these tempera- 

 tures on the recording drum as described in Experiment 3 above. The heart 

 being exposed 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 con- 

 tractions in good sequence and with a fairly rapid rate. Record the contrac- 

 tions on the smoked paper of the recording drum, together with a time trac- 

 ing 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 solu- 

 tion as a normal and compare with it the rate and amplitude of the contrac- 

 tions 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- 

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

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

 for a tracing on the smoked paper of the recording cylinder. Use a time- 

 marker. 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. 



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



