. 



PER1PI1ERIC ORGANS OF THE CIRCULATION. 157 



ward or downward direction, they are called positive or 

 negative, the former corresponding to the ventricular systoles, 

 and the latter to the repose of the heart. 



The sphygmograph of Marey, applied to the radial artery in 

 man, gives similar results. This is a registering apparatus, 

 noting down the impulsions of the artery imprinted upon it : 

 this is done by means of a small lever, applied to the artery 

 in the same manner as the finger of a physician when examin- 

 ing the pulse. The comparative duration of the systole and 

 the diastole is decided by the length of one of these waves, 

 as may also all the modifications of the circulation (Fig. 53). 

 It has thus been shown that the dicrotism of the pulse, 

 plainly sensible to the touch in some diseases, is only the 

 exaggeration of a dicrotism constantly taking place in the 

 normal condition of the blood wave. It consists in a slight 

 elevation, seen in the line of descent in the diagram (Fig. 

 53, in d), and is a sort of second pulsation coming after the 

 first. The investigations of Marey, Vivenot, and Duchek 



Fig 58. Sphygmographical tracing of the normal pulse. 



have rendered the mechanism of this phenomenon plain. It 

 was at first attributed to a returning wave, produced either 

 by the closure of the sigmoid valves or by the reflux of a 

 pulsation, which is reflected by the sharp division fold at 

 the bifurcation of the aorta into the two iliacs. Every fact 

 now seems to prove that the dicrotism is owing to the elas- 

 ticity of the artery, which, having been distended by the 

 ventricular systole, returns to its former size. The slight 

 ascension, interrupting the line of descent (Fig. 53, d), marks 

 the exact moment when, as we said before, the arterial elas- 

 ticity restores to the blood wave the force which it had stored 

 up, and which would be lost in a rigid tube, being expended 

 in friction (see p. 155, above). 1 By means of the sphygmo- 

 graph many other peculiarities of the circulation have been 

 observed : for instance, in deep inspirations the negative 

 waves increase in depth, while they diminish when forcible 

 expiration accompanies the strong pressure which takes place 



1 See Lorain, " Etudes de Medecine Clmique:" Du Pouls, 

 1870, in 8vo. 



