109 



359. Hill and Barnard's Sphygmometer. Hold the 

 sphygmometer in the vertical position, open the tap and press 

 the edge of the rubber bag upon the table until the fluid rises 

 to zero, then close the tap. By setting the fluid at zero before 

 each reading, errors due to variations of atmospheric pressure 

 and temperature are avoided. Having set the fluid at zero, 

 press the rubber bag upon the radial artery until the maximal 

 pulsation of the fluid is obtained. Read the pressure indicated 

 on the scale at that point. For example : Suppose the pulsa- 

 tion is maximal between 110 and 120 mm. Hg. then the mean 

 arterial pressure equals 115 mm. Hg. The normal average 

 pressure in young men is 110-120 mm. Hg. in the standing 

 and 100-110 mm. Hg. in the recumbent posture. The pulse 

 frequency does not as a rule vary more than five beats per 

 minute in the two positions. With this instrument the venous 

 pressure can also be obtained. On the back of the hand or 

 arm choose a vein free from anastomoses and press the sphyg- 

 mometer upon the peripheral end of this. Then empty the 

 vein centrally with the finger. Next gradually reduce the 

 pressure of the sphygmometer and note the exact pressure at 

 which the vein refills with blood. 



360. The Pneumograph. Apply this apparatus to the 

 thorax. Connect with a tambour and take a tracing on a 

 revolving drum. Study the curves. Does expiration occupy 

 a longer time than inspiration ? Compare with other mem- 

 bers of the group. 



Do not look at a tracing while it is being made, a person 

 unconsciously attempts to regulate the breathing so that a 

 perfect curve is made. Note the effect upon the curve of the 

 following phenomena : squeeze suddenly a rubber bulb held in 

 the right hand ; swallow a few mouthfuls of water ; hold the 

 breath while you count ten ; speak a few words ; laugh. Have 

 your co-worker indicate on the drum when each of these acts 

 are performed. Use a time marker marking half seconds. 



