260 THE CIRCULATION OF THE BLOOD 



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 for five minutes. 

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

 mine the heart-rate under the same conditions for as many different per- 

 sons as you can. Tabulate these rates to show age, sex, weight, and 

 height of the different classes of individuals, and compute general averages 

 for your sets. Count the rate in children and in aged. 



Note the effect on the averages obtained above after lying down for 

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

 minutes' brisk walk. Tabulate as directed. 



Count the heart-rate by successive 15 second periods immediately 

 upon standing from the reclining position and until the quarter minute 

 rates are constant; repeat immediately after two minutes of fast running. 

 Tabulate these results and compare the graphs obtained from several 

 different individuals. This method measures the character of the vascular 

 control in certain clinical states. 



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 on the fifth minute while sitting quietly. 

 A marked diurnal variation will usually appear. Determine these rates 

 on several individuals, 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, where 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. The 

 recording cylinder should travel at the rate of about two centimeters per 

 second. Take the time of the movements of the kymograph by an elec- 

 tric seconds magnet. The proper description should be written on the 

 smoked paper, the paper removed carefully and the whole record fixed in 

 shellac. 



Count the rate of the heart-beat from the record. Compute the time 

 of the cardiac systole and diastole, and of the pause at the end of the diastole 

 in seconds to three decimals. Records secured under different condi- 

 tions of exercise, etc., brought together in a table will usually show that the 

 higher heart-rates decrease the time of the cardiac cycle at the expense of 

 the diastole. In other words, the time of the systole remains fairly 

 constant, while the time of the diastole increases or decreases inversely 

 with the rate, a fact to which Hiirthle has drawn attention, figure 157. 



