60 PRACTICAL PHYSIOLOGY 



(a) Examine the manometer and see that, if there is a cap, it is 

 removed and that the mercury is at zero. 



(6) Enclose the upper arm of the subject in the armlet and, with 

 the arm horizontal and at the level of the heart, place one finger on 

 the radial pulse and raise the pressure in the instrument some 3 cm. 

 above the point at which the pulse disappears. (Take care not to 

 pull on the tube.} 



(c} Release the pressure gradually and note carefully the exact 

 height of the mercury at the moment when the pulse returns at the 

 wrist. This is the maximum systolic pressure. 



Repeat the observation, but instead of feeling the pulse listen over 

 the artery near the elbow with a binaural stethoscope, and note the 

 pressure at which a sound is first heard (maximum systolic pressure), 

 and go on slowly releasing till the sound disappears (diastolic 

 pressure). 



It is obvious that if the pressure under the armlet is just sufficient 



FIG. 57. Pulse tracing (sphygmogram) taken by Jacquet's sphygmograph. 



a d = the period of the pulse curve, 6 = the primary, c = the dicrotic wave. 

 Time marked in fifths of a second. 



to prevent the arterial pulse, i.e. the maximum systolic pressure, 

 from passing that it must give a measure of this systolic pressure. 



The lowest pressure in the artery, the diastolic pressure, which 

 occurs between the heart beats, is given by the disappearance of the 

 murmur or whiff-like sound, because this is caused by the con- 

 striction of the artery by the armlet when the pressure in it is 

 sufficient to compress the artery, but at the point when it becomes 

 insufficient the murmur disappears. 



(Read Arterial Blood Pressure in Text Book.) 



IV. Effect of Mental and Muscular Work on the Circulation and 



Respiration 



(This Experiment is better done after Respiration, p. 73.) 

 A. 1. Have ready the apparatus to record the respiration from 

 the nostril of a fellow student (p. 72, 6). 



2. Place the bag of the Riva Rocci apparatus round his arm. 



3. The subject holds the other hand out from the side and raises 

 and lowers it as directed. The observer determines at what level 

 of the hand the veins disappear while the subject is sitting still. 



4. Note the colour of the face. 



