MECHANICS OF THE' CIRCULATION IN THE VESSELS 125 



the volume of the part alters at any moment is a measure of the pulsa- 

 tory change of velocity in the arteries of the part. And by photo- 

 graphing the movements of the flame on a travelling sensitive surface, 

 the velocity-pulse is directly recorded. 



The mean velocity, like the mean blood-pressure, is more variable 

 in the large arteries near the heart than in the smaller and more 

 di stant arteries. 

 Dogiel found in 

 measurements 

 taken with the 

 stromuhr (a good 

 instrument for the 

 estimation of mean 

 speed), within a 

 period of two 

 minutes, velocities 

 ranging from over 

 200 mm. to under 

 100 mm. per second 

 in the carotid of the 

 rabbit, and from over 500 mm. to less than 250 mm. in the carotid of 

 the dog. Chauveau, with the dromograph, found the velocity in the 

 carotid of a horse to be 520 mm. per second during systole, 150 mm. 

 during the pause, 220 mm. during the period of the dicrotic wave. 



It is probable, however, that, if these numbers are at all accurate 

 for bloodvessels in the immediate neighbourhood of the heart, there 

 must be a rapid diminution in the velocity even while the arteries 

 are still of considerable calibre. For it has been found . by the 

 electrical method that, in anaesthetized dogs at any rate, as is shown 

 in the following table, the mean velocity between the origin of the 

 aorta and the crural artery in the middle of the thigh is usually less 

 than 100 mm. per second. 



Fig- 55- Photographic Record of the Velocity-Pulse ob- 

 tained by the Gas Tachograph (v. Kries). The upper 

 curve is the photographic representation of the move- 

 ments of the flame, and corresponds to the curve of 

 velocity. 



In I. the injecting cannula was in the descending part of the thoracic 

 aorta, in V. at the very origin of the aorta, and in II., III., and IV. 

 in the left ventricle. 



