ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



81 



applied with a pressure sufficient to flatten the artery, and then the 

 pressure should be diminished until the maximal excursion is obtained. 

 We have no means of accurately reading the pressure of the spring 



FIG. 78. Impulse curve of boy aged 15. The moments when the heart-sounds were 

 heard are marked. Time rrarked in fifths of a second. (L.H.) 



or the changes of pressure indicated by the pulse curve. The in- 

 strument gives us the form of the pulse curve only. When the smoked 

 paper is in position, and the writing style placed upon it, and the 

 maximal excursion obtained, the clock is started and the record taken. 



Fio 79. Form ot impulse curve changed by altering the position of cardiograph. In 

 3 the chest wall is sucked in during the systolic output. Time marked in fifths 

 of a second. (L.H.) 



The pulse curve consists of a primary and several secondary waves. 

 The primary wave is the wave of expansion produced by the systolic 

 output of the heart, and travels down the elastic arteries at a rate of 

 about 5-8 metres a second. The secondary waves are produced by the 



