MEASUREMENT OF THE VELOCITY OF THE BLOOD-STREAM. 181 



(2.) C. Ludwig and Dogiel (1867) devised a STROMUHR or RHEOMETER 

 for measuring the amount of blood which passed through an artery in a 

 given time (Fig. 82). It consists of two glass bulbs, A and B, of exactly 

 the same capacity. These bulbs communicate with each other, above, 

 their lower ends being fixed by means of the tubes, c and d, to the metal 

 disc, ee^ This disc rotates round the axis, X Y, so that, after a 

 complete revolution the tube, c, communicates with /, and d with g ; / 

 and g are provided with horizontally placed cannulae, h and Jc, which are 

 tied into the ends of the divided artery. The cannula, h, is fixed in 

 the central end, and Jc 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. 



(3.) Vierordt's Haematachometer 



(1858) consists of a small metal box (Fig. 

 83) with parallel glass sides. To the 

 narrow sides of the box are fitted an 

 entrance, 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 Volk- 

 mann's apparatus, has only a historical 

 interest.] 



I 



Fig. 83. 



Vierordt's Hsematachometer A,glass; 

 e, entrance; a, exit cannula; p, 

 pendulum. 



(4.) Chauveau and Lortet's (DromOgraph) (I860) is constructed on the same 

 principle. A tube, A, B (Fig. 84) of sufficient diameter, with a side-tube fixed to 

 it, C, which can be placed in connection 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 pen- 

 dulum, a, &, with a long index, 6, projects into the tube, i.e., into the blood- 

 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. 



The curve of the velocity may be written off on a smoked glass, 



