BLOOD PRESSURE MODEL 



423 



tubes are thick, it is advisable to aid the eye by looking along a glass 

 plate held at right angles to the tube. The tubes have a bore of one 

 square mm. and are divided into 100 equal parts. The reading multiplied 

 by 2 will give the volume of corpuscles in 100 parts of blood. The 

 function of the Muller's fluid is to retard clotting and to fix the red 

 corpuscles in their natural size. 



48. Blood Pressure Model, (a) General distribution. Examine the 

 schema (Fig. 83) of the circulation given you and identify the parts repre- 

 senting arteries, capillaries and veins. Disconnect the rubber ball H and 

 the two Bunsen valves V, V. Attach the arterial tube A to the water 

 supply and lead the tube from G to the sink. Cautiously turn on the water 

 and measure the pressure in the arteries (at B), and in the veins (at E). 

 (It is more economical to have single vertical tubes at B and E, the pressures 

 read off in mm. of water may be calculated in mm. of mercury.) 



Arterial BP 



FIG. 83. Schema of the Circulation. 



Note^the'effect of (a) varying the force of inflow by manipulation of the 

 water tap, (b) varying the resistance to flow by tightening the clip at D. 

 With a steady pressure over its whole length, compress G and note altera- 

 tion in manometer levels. 



(b) Pulse. Fill with water and replace H and V-V in circuit. Gently 

 compress and relax H at regular rhythmic intervals of about a second. 

 Note the effect of this upon the arterial and venous pressures. Study the 

 further effect of constricting D. 



(c) Place a finger on A and note the expansion with each contraction 

 of H. Study the same thing on D and on f. 



49. (a) Conduction of Sound Waves by the Cranial Bones. Place a 

 vibrating tuning fork in the region of the interparietal suture. From where 

 does the sound apparently come ? Place the tip of the finger into the 

 auditory meatus of one ear and then block both ears. Explain. 



(b) Binaural Localisation of Sound. With the eyes closed listen to the 

 ticking of a watch through a binaural stethoscope. Pinch one of the 

 tubes to prevent transmission of sound to one ear. Release and repeat 

 with other tube. 



50. Vowel Sounds by Percussion. Place the mouth in the position 

 necessary for the pronunciation of the various vowels and then percuss 



