94 



EXPERIMENTAL PHYSIOLOGY 



applied to the drum with a minimal amount of friction. This is 

 done by manipulating the adjusting screws on the tambour stands, 

 while the drum is moving slowly.* 



When the adjustment is completed the drum is stopped for a 

 moment so that the two levers may draw vertical lines showing 

 their relative positions (alignment marks). The drum is then 

 allowed to revolve at a medium speed and the tracings taken. 

 The speed should be as great as is consistent with a definite up- 

 stroke of the pulse. Alignment marks should be inscribed at 

 frequent intervals (by stopping the drum for a moment). A time 

 record (0.2 sec.) is added to the tracing with the drum revolving at 



FIG. 28. Simultaneous tracings of carotid and radial pulses. The rate of 

 transmission is determined by finding the difference between the beginning of 

 each pulse, after correcting for alignment of levers, and measuring off this distance 

 on the time tracing (l/50ths second.). 



the same speed as when the pulse tracings were being taken. A 

 vibrating spring provided with a writing point is used for taking 

 the time tracing. 



After the removal of the tracing from the drum, the distance of 

 the beginning of the upstroke is measured from its alignment mark 

 for each pulse curve (Fig. 28). The difference, interpreted in terms 

 of the time tracing, gives the rate at which the pulse wave travels 

 from the carotid to the radial artery. Note also the dicrotic notch 



This is more satisfactory than attempting to adjust to a stationary drum 

 because friction is diminished. Before starting the drum, however, make certain 

 that the tambours are so adjusted as to give the greatest possible movements. 



