MEASUREMENT OF THE VELOCITY OF THE BLOOD-STREAM. 



133 



cannula, h and k, which are tied into the ends of the divided artery. The cannula h is fixed 

 in the central end, and k in the peripheral end of the artery {e.g., carotid) ; the bulb, A, is 

 filled with oil, and B with defibrinated blood ; at a certain moment the communication through 

 h is opened, the blood flows in, driving the oil before it, and passes into B, while the defibrinated 

 blood flows through k into the peripheral part of the artery. As soon as the oil reaches m a 

 moment which is instantly noted, or, what is better, inscribed upon a revolving cylinder the 

 bulbs, A, B, are rotated upon the axis X, Y, so that B comes to occupy the position of A. The 

 same experiment is repeated, and can be continued for a long time. The quantity of blood 

 which passes in the unit of time (1 sec.) is calculated from the time necessary to fill the bulb 

 with blood. Important results are obtained by means of this instrument. 



[Suppose 50 c.cm. of blood are delivered in 100 sees., then 1 c.cm. flows through in 2 sees. 

 Suppose the sectional area of the artery to be 3 mm. As the velocity is measured by the ratio 



5000 

 of the quantity to the sectional area, then oTT7 = 159 mm. per second.] 



[As peptone injected into the blood prevents it from coagulating (dog), this fact has been 

 turned to account in using the rheometer. ] 



(3) Vierordt's Hsematachometer (1858) consists of a small metal box (fig. 113, I) with parallel 

 glass sides. To the narrow sides of the box are fitted an inlet e, and an exit cannula, a. In 

 its interior is suspended, against the entrance opening, a pendulum, p, whose vibrations may be 

 read off on a curved scale. [This instrument, as well as Volkmann's apparatus, has only an 

 historical interest.] 



(4) Chauveau and Lortet's Dromograph (1860) is constructed on the same principle. A tube 

 A, B (fig. 113), of sufficient diameter, with a side tube fixed to it, C, which can be placed in con- 

 nection with a manometer, is introduced into the carotid artery of a horse. At a a small piece 

 is cut out and provided with a covering of gutta-percha which has a small hole in it ; through 

 this a light pendulum, a, b, with a long index, b, projects into the tube, i.e., into the blood- 



Fig. 113. 

 I. Vierordt's hsematachometer. A, glass ; e, entrance ; a, exit cannula ; p, pendulum. II. 

 Dromograph. A, B, tube inserted in artery ; C, lateral tube connected with a manometer ; 

 b, index moving in a caoutchouc membrane, a ; G, handle. III. Curve obtained by 

 dromograph. 



current, which causes the pendulum to vibrate, and the extent of the vibrations can be read off 

 on a scale, S, S. G is an arrangement to permit the instrument to be held. Both this and 

 the former instrument are tested beforehand with a stream of water sent through them with 

 varying velocities. 



(5) Cybulski's Photohaematachometer. When fluid flows into a tube (fig. 114, II, de) in the 

 direction of the arrow, the fluid stands higher in the manometer p than in m. The tube my 

 indicates the lateral pressure, but px gives this plus the velocity of the fluid (p. 89). The 

 velocity of the current may be estimated from the difference in the level in the two tubes. 



Pitot's tube as used by Cybuhki is bent at a right angle (I, cp), the end c being inserted and 



