CIRCULA T1ON. 103 



2. Preparation. First, make two manometers whose dis- 

 tal limb shall be 40 cm. long, and proximal limb 30 cm. 

 with a horizontal shoulder 5 cm long. Second, 

 draw out the two limbs of the medium Y tube 

 until they are about the same in size as the 

 small tubing (Fig. 18). Third, construct the 

 FIG. 18. artificial circulatory system according to Fig. 17. 

 3- Operation. First, supply the manometers with mercury 

 so that there will be 12 to 15 cm. in each limb of the 

 arterial manometer, and 5 to 10 cm. in each limb of the 

 venous manometer. If the class is not familiar with the 

 use and interpretation of the manometer, the demonstra- 

 tor should lead them to discover all of its essential 

 features. Second, the whole system should be filled 

 with water and freed from air before the observations 

 begin. Third, care should be taken that no stoppage in 

 the system occurs; otherwise the mercury may be 

 thrown out of the manometers and lost. 

 4. Observations. 



a. The manometer (mercurial). 



(1) Find the actual pressure when the mercury in 

 the distal column stands 6 cm. higher than that in 

 the proximal column. Derive the following for- 

 mula: Actual pressure=13.6 TT r 2 (2 m ^), when 

 r=radius of column of mercury, and m the rise of 

 mercury in the distal limb of the manometer. 



(2) Find the pressure per square cm. where the ob- 

 servation is the same. Derive the following formula: 

 Pressure per unit area = 26.2 m. 



(3) Which of these data (actual pressure or pressure 

 per unit area) would be the more valuable to record ? 



(4) After the arterial circulatory system has been 

 freed from air and is at rest, do the proximal and 

 distal columns of mercury stand at the same level? 



