MAREY'S SPHYGMOGRAPH. 129 



and he succeeded with this instrument in showing the existence of the double- 

 beat (dicrotism) in the normal pulse (1850). 



(3.) Vierordt's Sphygmograph (1855). In this, one of the earliest sphygmo- 

 graphs, Vierordt departed from the principle of a fluctuating fluid column, and 

 adopted the principle of the lever. Upon the artery rested a small pad, which 

 moved a complicated system of levers. At first he used a straw six inches long, 

 which rested on the artery. The point of one of the levers inscribed its movements 

 upon a revolving- cylinder. This instrument was soon discarded. 



(4.) Marey's Sphygmograph consists of a combination of a lever 

 with an elastic spring. It consists of an elastic spring (Fig. 45, A) 

 fixed at one end, 2, free at the other end, and provided with an ivory 

 pad, y, which is pressed by the spring upon the radial artery. On 

 the upper surface of the pad there is a vertically-placed fine toothed 

 rod, k, which is pressed upon by a weak spring, e, so that its teeth 

 dove-tail with similar teeth in the small wheel, t, from whose axis 

 there projects a long, light, wooden lever, v, running nearly parallel 

 with the elastic spring. This lever has a fine style at its free-end, s, 

 which writes upon a smoked plate, P, moved by clock-work, U, in front 

 of the style. Marey's instrument, as improved by Mahomed and others, 

 has been very largely used. 



Fig. 45. 



Scheme of Marey's sphygmograph A, spring with ivory pad, y, which rests on 

 the artery ; e, weak spring pressing k into t ; v, writing lever ; P, piece of 

 smoked glass or paper moved by clock-work, U ; H, screw to limit excursion 

 of A ; s, arrangement for fixing the instrument to the arm of the patient, 



[Its more complete form, as in Fig. 46, where it is shown applied to the arm, 

 consists of (1.) a steel spring, A, which is provided with a pad resting on the 

 artery, and moves with each movement of the artery; (2.) the lever, C, which 

 records the movement of the artery and spring in a magnified form on the smoked 

 paper, G ; (3.) an arrangement, L, whereby the exact pressure exerted upon the 

 artery is indicated on the dial, M (Mahomed) ; (4.) the clock-work, H, which 

 moves the smoked paper, G, at a uniform rate ; (5.) a frame-work to which the 

 various parts of the instrument are attached, and by means of which the instru- 

 ment is fastened to the arm by the straps, K, K (Byrom Bramwell). 



[Application. In applying the sphygmograph, cause the patient to seat himself 

 beside a low table, and place his arm on the double-inclined plane (Fig. 46). In 

 the newer form of instrument, the lid of the box is so arranged as to unfold to 

 make this support. The fingers ought to be semi-flexed. Mark the position of 

 the radial artery with ink. See that the clock-work is wound up, and apply the 



9 



