90 A MANUAL OF PHYSIOLOGY 



the pulse-wave, and this extension may be far more con- 

 spicuous than the lateral dilatation. This is particularly 

 seen when one point of the vessel is fixed and a more distal 

 point offers some obstruction to the blood-flow, as at a 

 bifurcation, or in an artery which has been ligatured and 

 divided. 



By means of the sphygmograph, the lateral movements of 

 the arterial wall, or, rather, in man, the movements of the 

 skin and other tissues lying over the bloodvessel, can be 

 magnified and recorded. It would be very unprofitable to 

 enumerate all the sphygmographs which ingenuity has in- 

 vented and found names for. The first rude attempt to 

 magnify the movements of the pulse was made by loosely 



FIG. 26. SCHEME OF MAREY'S SPHYGMOGRAPH. 



A, Toothed wheel connected with axle H, and gearing into toothed upright R 

 C, ivory pad which rests over bloodvessel and is pressed on it by moving G, a screw 

 passing through the spring J ; E, writing-lever attached to axle H, and moved by its 

 rotation ; E writes on D, a travelling surface moved by clockwork F. 



attaching a thin fibre of glass or wax to the skin with a 

 little lard, in order to demonstrate the venous pulse which 

 appears under certain conditions, Vierordt improved on 

 this by using a counterpoised lever writing on a blackened 

 surface. But the inertia of the lever was so great that the 

 finer features of the pulse were obscured. In all modern 

 sphygmographs there is a part, usually button-shaped, which 

 is pressed over the artery by means of a spring, as in Marey's 

 and Dudgeon's sphygmographs, or by a weight, or by a 

 column of liquid. In Marey's instrument, the button acts 

 upon a toothed rod gearing into a toothed wheel, to which 

 a lever, or a system of levers, is attached. The lever has 

 a writing-point which records the movement on a smoked 

 plate, or a plate covered with smoked paper, drawn uni- 

 formly along by clockwork. Brondgeest's pansphygmograph 

 is a particular application of Marey's tambours, for receiving 



