382 THE MECHANICS OF THE CIRCULATION, HEMODYNAMICS 



by Marey, 1 to which the name of sphygmograph has been given. 

 Although variously modified in subsequent years, the principle in- 

 volved in its construction has not been changed. 



A pellotte, attached to a steel spring, is placed upon the skin over the radial 

 artery in such a way that the pulsations of this blood-vessel are communicated 



FIG. 199. SCHEMA ILLUSTRATING THE SPHYGMOGRAPH OF MAREY. 

 B, pelotte applied to blood-vessel; W, toothed wheel fitting into toothed rod; R, 

 the up and down movements of this rod give rise to a back and forth movement of the 

 wheel; to its axis is attached a writing lever (L) registering its excursions upon a 

 kymograph (K). 



to it directly. But a,s the excursions executed by the arterial wall and over- 

 lying tissues are relatively small, it is necessary to magnify the movements of the 

 sphygmograph considerably by increasing the leverage of its writing lever. The 

 latter must be very light and a certain resistance must be imparted to it, otherwise 



FIG. 200. FIG. 201. 



FIG. 200. THE DUDGEON SPHYGMOGRAPH IN POSITION. 



FIG. 201. DIAGRAM ILLUSTRATING THE ACTION OF DUDGEON'S SPHYGMOGRAPH. 



(Howell.) 



The lever of the Dudgeon sphygmograph: P, the button of the spring F, to be placed 

 upon the artery. The movement is transmitted to the lever, Fi, and thence to the 

 bent lever, Fz, the movement of which is effected through the weight, g. The writing 

 point S, of this lever makes the record on the smoked surface, A. 



its movements may be much exaggerated by inertia. In the instrument of 

 Czermak, 2 the place of the recording lever is taken by a mirror by means of which 

 a beam of light is reflected upon sensitive paper moved at an appropriate speed. 



1 Jour, de la physiol., iii, 1860. 



2 Sitzungsb. der Akad. der Wissensch., Wien, 1863. 



