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HANDBOOK OF PHYSIOLOGY. 



Estimation of the Velocity. Various instruments have been devised for 

 measuring the velocity of the blood-stream in the arteries. Ludwig's Stromuhr 

 (fig. 189) consists of a U-shaped glass tube dilated at a and a', the ends of 

 which, h and i, are of known calibre. The bulbs can be filled by a common 

 opening at k. The instrument is so contrived that at b and V the glass part is 

 firmly fixed into metal cylinders, attached to a circu- 

 lar horizontal table, c c', capable of horizontal move- 

 ment on a similar table d d' about the vertical axis 

 marked in figure by a dotted line. The opening in c c', 

 when the instrument is in position, as in fig., cor- 

 responds exactly with those in d d' ; but if c c' be 



Fig. 190. 



Fig. 189. Ludwig's Stromuhr. 



Fig. 190. Diagram of Chauveau's Instrument, n. Brass tube for introduction into the lumen of 

 the artery, and containing au index needle, which passes through the elastic membrane in its side, 

 and moves by the impulse of the blood-current, c. Graduated scale, for measuring the extent of 

 the oscillations of the needle. 



turned at right angles to its present position, there is no communication be- 

 tween h and a, and i and a', but h communicates directly with i ; and if 

 turned through two right angles c' communicates with d, and c with d '.', and 

 there is no direct communication between h and i. The experiment is per- 

 formed in the following way : The artery to be experimented upon is divided 

 and connected with two canulse and tubes which fit.it accurately with h and 

 i h the central end, and i the peripheral ; the bulb a is filled with olive oil up 

 to a point rather lower than k, and a' and the remainder of a is filled with 

 defibrinated blood ; the tube on k is then carefully clamped : the tubes d and 

 d' are also filled with defibrinated blood. When everything is ready, the blood 

 is allowed to flow into a through h, and it pushes before it the oil, and that 

 the defibrinated blood into the artery through i. and replaces it in a' ; when the 

 blood reaches the former level of the oil in a', the disc c c' is turned rapidly 

 through two right angles, and the blood flowing through d into a' again dis- 

 places the oil which is driven into a. This is repeated several times, and the 

 duration of the experiment noted. The capacity of a and a' is known ; the 

 diameter of the artery is also known by its corresponding with the canulas of 

 known diameter, and as the number of times a has been filled in a given time 

 is known, the velocity of the current can be calculated. 



