272 THE CIRCULATION OF THE BLOOD 



small caliber is introduced into the end in order to produce high resistance 

 to the outflow. Determine the amount of resistance necessary to produce 

 a constant outflow when the pump has a rate of 72 beats per minute. 



In this experiment what effect is produced on the outflow if the rate 

 of the pump is varied? if the force of the stroke is varied? if the elasticity 

 of the rubber tube representing the artery is varied? If the resistance 

 represented by the size of the glass tube at the outflow is varied? 



17. The Arterial Pulse. The form of the arterial pulse maybe taken 

 by one of the various sphygmographs applied to the radial artery at the 

 wrist or the common carotid in the neck. If the tambour method is used, 

 apply a sphygmographic tambour on the wrist adjusting the central 

 pressure over the radial artery. Fasten it in place by the proper bands, 

 adjusting the tension by flexing the wrist. Connect the receiving tambour 

 with a delicately balanced, small-sized recording tambour, which should 

 write its movements on a cylinder revolving at the rate of i to 2 cm. per 

 second. 



A convenient clinical instrument is the Dudgeon or the Jacquet 

 sphygmograph. These are to be applied at the wrist and give tracings 

 showing delicate variations in the form of the pulse wave with great 

 magnification and a considerable degree of accuracy. Make a comparison 

 of the form of the pulse wave from tracings taken from at least six different 

 individuals. 



The sphygmogram from the carotid artery may best be taken by 

 applying an air sphygmograph to the neck over the carotid and fastening 

 it in position by a spring. Record by the tambour method. 



1 8. The Rate of Propagation of the Pulse Wave. Apply tambour 

 sphygmographs to the carotid in the neck and to the radial at the wrist, and 

 make simultaneous records on a drum, adjusting the writing levers 

 of the two recording tambours in an exact vertical line. Let the recording 

 drum travel at the speed of 2 cm. or more per second, and record the speed 

 by a 50 double-vibration tuning-fork. The carotid pulse will be found to 

 precede the radial pulse by the fraction of a second. This short interval, 

 which can be determined in thousandths of a second by comparison with 

 the time tracing below, represents the time required for the pulse wave to 

 traverse the distance from the carotid to the radial. Measure the distance 

 used in the experiment and calculate the rate of propagation in centi- 

 meters per second. 



If the writing points of the recording levers in this experiment are made 

 of very delicate strips of note paper or of thin photographic film celluloid, 

 so as to offer little resistance to the surface of the drum, the detail of the 

 pulse wave at the two points will be accurately transcribed and may be 

 compared. 



19. The Capillary Circulation. The capillary circulation is best 



