MOVEMENT OF THE BLOOD IN THE ARTERIES. 



333 



three different points of its length the tube is placed under the control of a 

 Sphygmograph, the levers of which, 1 1' I", register their movements on the 

 drum c in such a manner that their tracings may be exactly parallel and 



Fie. 135. 



comparable with one another. Fig. 136 shows such a triple tracing after 

 the india-rubber bag has been for a few times rhythmically compressed. It 

 is here evident that, as indicated by the oblique dotted line, the period at 

 which the maximum of tension is attained, is latest iu that portion of the 



FIG. 136. 



tube which is most distant from the impelling organ, and a certain, though 

 minute retardation occurs in the passage of the wave through the column of 

 liquid. The actual amount of this retardation has been carefully investi- 

 gated by Czermak, 1 with the aid of his photo-sphygmograph, in which the 

 fluctuations of a ray of light reflected from a small mirror placed over the 

 radial artery are registered on a screen of prepared photographic collodion. 

 The mean of a series of twenty experiments, showed that the pulse in the 

 radial artery at the wrist was 0.18 sec. earlier than in the dorsal artery of 

 the foot ; whilst the shock of the heart occurred 0.159 of a sec. earlier than 

 the pulsation at the wrist, and 0.087 sec. earlier than the pulse in the 

 carotid. It, therefore, takes about th of a second for the primary pulse- 

 wave to travel from the heart to the foot, and estimating this distance 

 roughly at five feet, the rate of the pulse-wave is about thirty feet a second, 

 with which Weber's estimate (28.5 feet) closely agrees. The rate of the 

 pulse-wave is, of course, to be carefully distinguished from the velocity of 



1 Mittheilungen aus clem Priv.it-Luboratorium, Heft 1, 1864, p. 27. 



