VELOCITY AND PRESSURE OF BLOOD-FLOW. 



437 



merit different from those at the beginning. By means of the stromuhr 

 however, this experiment can be made, with this alteration, how- 

 ever, that the blood that flows from the central end of the cut artery 

 is returned to the peripheral end of the same artery, so that the 

 circulation is not blocked nor deprived of its normal volume of 

 liquid. The instrument, as is explained in the legend of Fig. 174, 

 measures the volume of blood that flows out of the cut end of an 

 artery in a definite time. The calculation for velocity is made as 

 follows: Suppose that the capacity 

 of the bulb is 5 c.c, and that in the 

 experiment it has been filled 10 

 times in 50 seconds, i. e., the bulbs 

 have been reversed 10 times; then 

 obviously 10 X 5 or 50 c.c. have 

 flowed out of the artery in this 

 time, or 1 c.c. in 1 second. The 

 diameter of the vessel can be meas- 

 ured, and if found equal, say, to 2 

 mms., then its cross-area is izr 1 = 

 3.15 X 1 = 3.15. Since 1 c.c. equals 

 1000 c.mm., the length of our cyl- 

 inder of blood would be given by 



1000 



the quotient of ^-^ = 317 mms. 

 So that the blood in this case was 

 moving with the velocity of 317 

 mms. per second. Another instru- 

 ment that has been employed for 

 the same purpose is the dromograph 

 or hemodromograph of Chauveau. 

 This instrument is represented in 

 the accompanying figure (Fig. 175). 

 A rigid tube (p-c) is placed in the 

 course of the artery to be examined. 

 This tube is provided with an offset 

 (a) the opening of which is closed 

 with rubber dam (m). The rubber 

 dam is pierced by a needle the lower 

 end of which terminates in a small 



plate lying in the tube (pi). When the instrument is in place and 

 the blood is allowed to stream through the tube, it deflects the 

 needle, which turns on its insertion through the rubber as a ful- 

 crum. The angle of deflection of the free end of the needle may 

 be measured directly upon a scale or it may be transmitted 

 through tambours and recorded upon a kymographion. The in- 

 strument must, of course, be graduated by passing through it cur- 



> 



Fig. 175. Chauveau's hemodromo- 

 graph (after Langendorff). The tube, 

 p-c, is placed in the course of an ar- 

 tery, the blood after removal of clamps 

 flowing in the direction shown by the 

 arrow. The current strikes the plate, 



a 



pi, and forces it to an angle varyin 

 with the velocity. The movement 

 pi is transmitted through the stem, n, 

 which moves in a rubber membrane, 

 m. The angular movement of the 

 projecting end of n may be measured 

 directly or may be made to act upon a 

 tambour, as shown in the figure, and 

 thus be transmitted to a recording 

 drum. 



