PULSE TRACING 93 



Start the drum. Pump up the pressure in the armlet 

 till the pulse ceases to show on the tracing. Then let out 

 slowly the air from the armlet. As the pressure falls the 

 pulse reappears on the tracing. On the tracing measure 

 with compasses the height of the column of Hg at which 

 the pulse tracing ceased and began again. Compare the 

 result with that obtained in 1. 



4. Keeping the apparatus as in 3 determine how 

 long (about) you can hold your breath. Then set the 

 drum in motion, and in 5 to 10 seconds pump up the 

 armlet till the pulse tracing just ceases. Continue to 

 hold the breath for some time longer, it will be found 

 that the pulse tracing reappears, to disappear again soon 

 after respiration begins. The reappearance of the pulse 

 wave is due to increased blood pressure caused by the 

 increase of C0 2 in the blood. 



5. Use Hill's bulb sphygmomanometer, a diagram of 

 which is given in Fig. 27. 



Take the gauge G (cooling it if necessary to the tem- 

 perature of the room by holding it by the closed end 

 and waving it in the air) and dip the open end into the 

 coloured fluid given you (eosin in 1 p.c. sodium carbon- 

 ate). The fluid will rise to the level of the side hole, 

 the zero point. 



With the bulb half -full of air, slip the open end of the 

 gauge into the tube connected with the bulb. Place the 

 bulb on the wrist of A, and cover it with the left hand as 

 in the fig. ; whilst A holds the end of the gauge. 



With the first two fingers of the right hand, feel the 

 radial pulse of A. Press on the bulb, and note the pres- 

 sure on the gauge at which the pulse just disappears, 

 and then on relaxing slightly the pressure just reappears. 



