CHAPTER XIX 



Methods of Investigating the Circulation in the 

 Blood-Vessels 



THE chief methods used can be practised upon a long india-rubber 

 tube through which water is pumped from a low reservoir by a rubber 

 syringe actuated by some form of motor. After passing through the 

 system the fluid is again delivered into the reservoir; this represents 

 the capillary and venous systems. A mercury kymograph (Fig. 67) and 

 other manometers, such as Fick's C-spring (Fig. 68), Fick's straight- 

 spring, Hiirthle's tambour (Fig. 69) (as well as Lud wig's stromuhr 

 (Fig. 70), and other instruments for measuring or estimating velocity) 

 may be connected by means of T-tubes with the main india-rubber 

 tube. The use of each instrument is to be studied separately, the 

 others being temporarily shut off by screw-clips. Notice how the 

 movement of any of the recording manometers may be damped by 

 partially closing the tube connecting it with the main system. 

 Observe the effect upon the pressure within the system (1) of increasing 

 either the rate of the pump or the amount delivered at each stroke ; 

 (2) of diminishing or enlarging the outflow from the main tube by a 

 screw-clip. This is equivalent to contraction or dilatation of the 

 arterioles. Take a tracing with each form of manometer. Also 

 record the amount of fluid passing through the stromuhr in one minute. 

 Measure the diameter of the artery in whose course the instrument is 

 inserted, and calculate from these data the velocity of flow. The 

 velocity is found by dividing the amount flowing through the instru- 

 ment in a second by the sectional area of the vessel ( V = g j. 



Plethysmography. The arm of a subject (who is to be seated com- 

 fortably) is placed in a Mosso plethysmograph (Fig. 71, p. 88), and this 

 is allowed to rest on a table or in a sling. The junction with the arm 

 is made by a broad rubber band. The interior of the plethysmograph 

 is connected by rubber tubing with a recording tambour or piston- 

 recorder; the whole is to be air-tight. The lever of the recorder 

 registers respiratory and cardiac movements upon the smoked surface, 

 since these movements produce changes in general arterial pressure, 



