VELOCITY AND PRESSURE OF BLOOD-FLOW. 



499 



the base line, is much greater than in the record obtained with the mercury 

 manometer, Fig. 193. 



In the optical manometers the errors due to the mass and friction of levers 

 are avoided by making use of a beam of light which is reflected from a small 

 mirror attached to a segment-capsule. The construction of the segment-cap- 



S\> 



C-M 



190 



too 



L<L 



Fig. 199. Curve showing the results of actual measurement of systolic, diastolic, and 

 mean pressure (lateral pressures) along the a9rta and femoral of the dog. The branches 

 through which the lateral pressures were obtained are indicated as follows: Sb, Left sub- 

 clavian ; C-M, celiac and superior mesenteric ; R, left renal ; F, left femoral (Ellenberger 

 and Baum), external iliac; P, profunda branch of femoral; S, saphena. The pressure in 

 millimeters is given along the ordinates to the left. It will be noted that the mean and 

 the diastolic pressures remain practically the same through9Ut the descending aorta and 

 into the femoral. The systolic pressure shows a marked increase at the lower end of 

 the aorta and then falls off rapidly. The pulse pressure at the inferior end of the descend- 

 ing aorta is much larger than at the arch. (Dawson.) 



eule and a diagram of the optical method of using it are shown in Fig. 198a.* 



The method that depends upon the use of maximum and minimum valves 

 may be understood by reference to Fig. 197. On the path between the artery 



* See Wiggers, " Modern Aspects of the Circulation in Health and Disease," 

 1915; also "Journal of the American Medical Association," April 17, 1915. 



