LABORATORY EXPERIMENTS ON THE CIRCULATION 249 



LABORATORY EXPERIMENTS ON THE CIRCULATION. 



1. The Rate of the Human Heart-beat. Determine the rate of 

 the heart-beat per minute by counting the radial pulse, using a watch for 

 the time. Make the determination after sitting quietly in a chair for five 

 minutes. Take the average of at least ten determinations for your own case. 

 Determine the heart-rate under the same conditions for as many different 

 persons as you can. Tabulate these determinations in a table which shows 

 age, sex, weight, and height of the different individuals, and compute a 

 general average for your entire set. Count the rate in children and in aged. 



Note the effect on the averages obtained above after the person lies down 

 for five minutes, after standing quietly for the same time, and after five 

 minutes' brisk walk. Tabulate as directed. 



Count the heart-rate immediately after two minutes' fast running, allow- 

 ing the person immediately to sit in a chair. Count the rate by two-minute 

 intervals until there is a complete return to the normal, as determined above. 

 Tabulate these results and compare the figures obtained from several dif- 

 ferent individuals. 



Count your own heart-rate at one- hour intervals during one entire day, 

 giving special attention to the rate just before and just after meals, but in 

 every case make the count after sitting quietly for five minutes. A marked 

 diurnal variation will usually appear. Determine these rates on several indi- 

 viduals, and tabulate as before. 



2. Human Cardiogram. Apply a Burdon- Sanderson cardiograph 

 to the thorax over the point between the fifth and sixth ribs of the left side, 

 at which point the cardiac impulse is felt most distinctly. Connect the 

 cardiograph with a recording tambour, Marey's form, adjust the tension 

 of the cardiograph and the pressure of the air within the system, and take a 

 tracing of the movements of the lever of the recording tambour on the smoked 

 paper of the kymograph. The kymograph cylinder should travel at the rate 

 of about two to three centimeters per second. Take the time of the move- 

 ments of the kymograph by means of an electric magnet connected with an 

 electric clock beating seconds. After the record is secured the proper de- 

 scription should be written with a pencil on the smoked paper, and the paper 

 removed from the kymograph carefully and the whole record fixed in shellac. 



When the record is dry, count the rate of the heart-beat from the record 

 and measure the time of the cardiac systole and diastole, and the time of 

 pause at the end of the diastole. If these facts are taken from records secured 

 under different conditions of exercise, etc., as outlined in the preceding ex- 

 periment, then they may be brought together in a table for convenience of 

 inspection. A comparison of such results will usually show that with the 

 higher heart-rates the decrease of the time of the cardiac cycle is at the ex- 

 pense of the time of the diastole; in other words, the time of the systole re- 



