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HAND-BOOK OF PHYSIOLOGY. 



the aorta. Thus the velocity of blood in the capillaries is at least j^-g- of 

 that in the aorta. 



Velocity in the Arteries. The velocity of the stream of blood is 

 greater in the arteries than in any other part of the circulatory system, 

 and in them it is greatest in the neighborhood of the heart, and during 

 the ventricular systole; the rate of movement diminishing during the dias- 

 tole of the ventricles, and in the parts of the arterial system most distant 

 from the heart. Chauveau has estimated the rapidity of the blood- 

 stream in the carotid of the horse at over 20 inches per second during the 

 heart's systole, and nearly 6 inches during the diastole (520 150 mm.). 



Estimation of the Velocity. Various instruments have been devised 

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

 f "ffiromuhr" (Fig. 142) consists of a U-shaped glass tube 



dilated at a and #', and whose extremities, Ji 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, 

 which are fixed into a circular horizontal table, c c' , capa- 

 ble of horizontal movement 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., corresponds exactly with those in d d'\ but if c c r 

 be turned at right angles to its present position, there 

 is no communication between Ji 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 connection between h 

 and i. The experiment is performed in the following 

 way: The artery to be experimented upon is divided 

 and connected with two cannulse and tubes which fit it 

 accurately with h and i Ji 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 defibri- 

 nated 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 Ji, and it pushes before it the oil, 

 and that the defibrinated blood into the artery through i, and replaces 

 it in #'; 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 displaces 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 cannulae 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. 



FIG. 142. Ludwig's 

 Stromuhr. 



