202 THE CIRCULATION OF THE BLOOD 



other the distal tube being bent down stream, records merely lateral 

 pressure. A photographic record of the movement of the fluid in the 

 two tubes gives the velocity pulse (see Fig. 57). For physiological pur- 

 poses the form of apparatus used is constructed as shown in Fig. 58. 



Palpable Pulse. To secure a record of the palpable pulse, the so- 

 called sphygmograph is employed, although a tambour having a button 

 in the center which is made to press on the artery may also be em- 

 ployed. The commonest form of sphygmograph is that known as 

 Dudgeon's (Fig. 59). It consists of a small button connected with a 

 spring, the movements of which are transmitted and magnified by means 

 of a system of levers connected with a writing point arranged so as 

 to inscribe its movements on a moving surface. 



The Analysis of the Curve 



The general contour of the pulse waves taken by any of the above 

 methods are in general very much the same. The pressure and velocity 



Fig. 60. Pulse tracing (sphygmogram) taken by sphygmograph. a d, the period of the pulse 

 curve; b, the primary; c, the dicrotic wave. Time marked in fifths of a second. (From Prac- 

 tical Physiology.) 



pulse curves are, however, not usually taken for the purpose of observ- 

 ing the contour of the wave but rather for measuring the difference in 

 pressure or velocity actually produced during each pulse. It is a record 

 of the palpable pulse that is usually employed for studying the contour 

 of the wave and the presence of secondary waves. A record of the pal- 

 pable pulse wave (Fig. 60) shows two separate waves on the descending 

 limb of the main wave. If a large number of similar pulse curves are 

 taken from different individuals or from the same individual under 

 different conditions, it will be found that of these two waves the secQnjj 

 one is by far the more constant ; and if the waves are timed in relation 

 ship to the heart sounds, this second wave always occurs immediately 

 after the second sound, allowance, of course, being made for the time 

 required for the pulse to be transmitted from the heart to the artery 

 from which the pulse tracing is being taken. If the observation is 

 made very carefully, it can indeed be shown that the second sound cor/ 

 responds exactly to the notch which precedes this wave. The waves that 



