CH. XXII.] 



C1IAUVEAU S DKOMOGRAPH 



287 



carotid are practically identical, but that the maximum systolic 

 pressure is actually higher in the crural than in the carotid ; in the 

 dog the difference may amount to as much as 60 mm. mercury. 

 This difference is partly to be explained in that the carotid arises 

 from the aorta at a right angle, and therefore gives the true pressure- 

 liead, while the crural, to a considerable extent, faces the stream, and 

 therefore gives both pressure-head and velocity-head. 



Unfortunately, at present no really satisfactory measurements are 

 at hand from which the pressure gradient can be determined. 



Cybulski's instrument is 

 not the only one we possess 

 for obtaining records of the 

 velocity-pulse. Vierordt in- 

 vented a haemo - tachometer, 

 employing the principle of the 

 hydrometric pendulum ; his 

 instrument was improved by 

 Chauveau. Chauveau's in- 

 strument is shown in fig. 252. 



It consists of a thin brass tube, a, 

 in one side of which is a small per- 

 foration closed by thin vulcanised 

 india-rubber. Passing through the 

 rubber is a fine lever, one end of 

 which, slightly flattened, extends 

 into the lumen of the tube, while 

 the other moves over the face of a 

 dial. The tube is inserted into the 

 interior of an artery, and ligatures 



applied to fix it, so that the "velocity pulse," i.e., the change of velocity with each 

 heart-beat, may be indicated by the movement of the outer extremity of the lever 

 on the face of the dial. 



In order to obtain the actual value of these movements in terms 

 of velocity, the instrument must be calibrated beforehand. The next 

 diagram, fig. 253, shows how the instrument may be adapted to give 



FIG. 252. Diagram of Chauveau's Dromograph. a, Brass 

 tube for introduction into the lumen of the artery, 

 and containing an index needle, which passes 

 through the elastic membrane in its side, and 

 moves by the impulse of the blood - current ; 

 c, graduated scale, for measuring the extent of the 

 oscillations of the needle. 



FIG. 253. Chauveau's Dromograph connected with tambours to give a graphic record. 



a graphic record. The movements of the pendulum are brought to 

 bear upon a tambour, B, which communicates by a tube with the 



