266 



PHYSIOLOGY 



CHAP. 



wave of central origin and centrifugal course which excludes the 

 hypothesis still maintained by some, that it arises in a peripheral 

 and centripetally reflected wave. This last hypothesis is also 

 irreconcilable with the fact that the secondary positive wave is 

 nearly always preceded by a negative wave which, as we shall see 

 immediately, can only be of central origin. 



Fn:. 10."). Spliyginograms from radial artery '(Sr), and changes produced by inhalation of 

 amyl nitrite (.S'V). (A. D. Waller.) 



The long experience of nearly half a century, during which 

 Marey's sphygmograph (or other sphygmographs which are only 

 modifications of this instrument) has been employed clinically, has 

 proved it to be of very little diagnostic value. We have for 

 many years insisted on this fact, and for the following reasons. 



FIG. 106. Marey's transmission sphygmograph applied to radial artery. This only differs from 

 the direct sphygmograph in that the movements of the button of the spring are not trans- 

 mitted by a lever, but by a receiving tambour, which then transmits them to a second 

 tambour writing upon the revolving drum of the kymograph. 



It is quite true that the sphygmogram is the true expression 

 of the form and magnitude of the pulsatile oscillations in pressure 

 in the artery to which the instrument is attached, but it is far 

 from representing their absolute values. Local arterial pressure is 

 indeed dependent on many variable factors : on the tension of the 

 spring, the elasticity and tone of the arterial walls, the amount 

 and degree of torpor in the surrounding soft parts. From all these 

 causes, the size of the pulse, i.e. the amplitude of the sphygmogram, 

 is in no definite ratio either with the volume of blood driven 

 from the heart to the arteries at every systole, nor with the height 



