334 THE CIRCULATION. 



the entire length of the tube, and that the whole time of a pulsation is 

 everywhere of equal duration. But near the commencement of the tube, 

 the expansion is wide and sudden, and occupies only a sixth part of the 

 entire pulsation, while all the rest is taken up by a slow reaction. At 

 more remote points the period of expansion becomes longer and that of 

 collapse shorter ; until finally, at a certain distance, the amount of ex- 

 pansion is reduced one-half, and at the same time the two periods are 

 completely equalized. 



Automatic Registration of the Arterial Pulse; the Sphygmograph. 

 The frequency and characters of the arterial pulse may be permanently 

 recorded by the use of a movable lever capable of registering its own 

 oscillations, and so arranged that it may be applied to any of the super- 

 ficial arteries in the living body. This instrument, which was first made 

 practically serviceable by the improvements of Marey, is the sphygmo- 

 graph. It consists of a small ivory plate, which is gently pressed upon 

 the artery by means of a fine spring, and which thus rises and falls with 

 each expansion and collapse of the arterial tube. The motion of the 

 plate is communicated to a vertical metallic rod touching the under sur- 

 face of the registering lever near its attached extremity. The oscillating 

 extremity of the lever, when the instrument is in operation, thus follows 

 the movements of the ivory plate, and registers faithfully upon the strip 

 of paper, the frequency and form of the arterial pulsations. 



The advantage of this instrument is, first, that the length of the lever 

 magnifies to the eye the extent of the arterial oscillations, and thus 

 enables us to perceive movements too delicate to be distinguished by 

 the touch alone ; and, secondly, that, each part of a pulsation being 

 permanently registered upon paper, the most evanescent changes in the 

 form of the artery may be afterward studied at leisure and compared 

 with each other. 



By the use of the sphygmograph it is shown, that, while there is a 

 general resemblance in the form of pulsation of different arteries, nearly 

 every vessel to which the instrument can be applied presents certain 

 peculiarities dependent on its size, position, and distance from the 

 heart. In the radial artery at the wrist, each pulsation consists of a 



Fi>. 112. 



TKACE 01- THE K ADI AL PULSE, taken by the Sphygmograph. 



sudden expansion of the vessel, indicated by a rapid upward movement 

 of the lever, making, in the trace, a straight, nearly A^ertical line. This 

 is followed by a gradual descent corresponding with the collapse of the 

 artery, until it reaches the lowest point of the trace, when the move- 

 ment of ascension again takes place, and so on alternately. The line 

 of descent, however, is not straight, like that of ascension, but is marked 



