268 



PHYSIOLOGY 



OHAl'. 



can be used for the i carotid, femoral, or other arteries, as also 

 Edgren's sphygmograph, or any kind of tympanum with an 

 elastic membrane kept stretched by a spiral spring, and provided 

 with an exploring button in the centre, which can be pressed 

 against the artery to be examined (Fig. 108). 



VIII. The comparison of cardiograms and sphygmograrns 

 simultaneously recorded on the same revolving cylinder gives all 

 the data necessary to establish the chief characteristics of the two 

 tracings. Those of Fig. 109 were obtained by Edgren on a healthy 

 youth of twenty-five. The various features of the cardiographic 

 curve (a, b, c, d, e,f, g, h, i) are indicated by vertical lines. Since 



Fio. 109. Cardiograms (C) and sphygmograms (S) of carotid of a healthy subject of 25. (Edgren. ) 

 n, b, c, d, e, /of the cardiograms correspond with the ], h], cj, </,, fj, }\ of the sphygmograms. 



these are obvious, they need no further description. After what 

 was said in the previous chapter (Fig. 80, p. 224) we know that the 

 point a corresponds with the onset of systole, when the first sound 

 of the heart begins to be heard, and the point / with the onset of 

 diastole, when the semilunar valves, which have already been 

 closed at the systolic dead point, are thrown into tension, and the 

 second sound develops. In the sphygmographic curve of the 

 carotid the point coinciding with a shows no marked feature. 

 The primary sphygniic wave which starts from the arterial orifice 

 first reaches the carotid at the point b' The interval ab', therefore, 

 represents the time taken up by the transmission of the pulse 

 wave from the arterial orifice to the carotid, plus the time of the 

 latent systole, i.e. that between the commencement of the con- 

 traction of the myocardium and the moment of the opening of the 



