178 



THE VASCULAR MECHANISM. 



the artery, near to the surface and with the support of the radius below so 

 that adequate pressure can be brought to bear by the lever on the artery, is 



FIG. 



Diagram of a Sphygmograph ('Dudgeon's). Certain supporting parts are omitted so that the mul- 

 tiplying levers may be displayed, a is a small metal plate which is kept pressed on the artery by the 

 spring b. The vertical movements of a cause to-and-fro movements of the lever c about the fixed 

 point d. These are communicated to and magnified by the lever e, which moves round the fixed 

 point/. The free end of this lever carries a light steel marker which rests on a strip of smoked 

 paper g. The paper is placed beneath two small wheels and rests on a roller which can be rotated 

 by means of clock-work contained in the box h. The paper is thus caused to travel at a uniform 

 rate. The screw graduated in ounces (Troy) is brought to bear on the spring b by means of a cam 

 and by this the pressure put on the artery can be regulated. The levers magnify the pulse-move- 

 ments fifty times. 



favorable for making observations. It can, of course, be applied to other 

 arteries. When applied to the radial artery some such tracing as that 



[Fio. 61. 



Marey's Sphygmograph : B, B is where the sphygmograph is applied to the arm ; R, spring 

 which rests upon radial artery ; V, screw for adjusting marking lever L ; H, clock-work ; P, smoked 

 paper upon which tracing is made ; r, small spring for causing descent of lever after raising.] 



shown in Fig. 62 is obtained. At each heart beat the lever rises rapidly and 

 then falls more gradually in a line which is more or less uneven. 



