272 CIRCULATION. 



sired. It consisted of a little square box made of glass, with 

 an opening at each, end, by which it was to be connected with 

 the artery. This is filled with water, and contains a pendu- 

 lum, which is struck by the current of blood. The deviations 

 of the pendulum are marked on a scale. After this has 

 been applied to an artery, and the extent of movement of 

 the pendulum noted, it is removed from the vessel and con- 

 nected with an elastic tube, in which a current of water is 

 made to pass with a degree of rapidity which will produce 

 the same deviation as occurred when the instrument was con- 

 nected with the blood-vessel. The rapidity of the current in 

 this tube may be easily calculated by receiving the fluid in a 

 graduated vessel, and noting the time occupied in discharg- 

 ing a given quantity. By this means we ascertain the 

 rapidity of the current of blood. By means of a needle 

 attached to the pendulum, the oscillations could be regis- 

 tered on a revolving cylinder of paper, and the mean velocity 

 taken. 



"With this instrument, Yierordt estimated the mean velo- 

 city of blood in the carotid at 10'2 inches per second. Chau- 

 veau, who invented an instrument which we will describe 

 presently, found the instrument of Vierordt not sufficiently 

 sensitive, and requiring so much care and precaution in its 

 use as to essentially diminish the value of its results. 



The best instrument for measuring the rapidity of the 

 circulation in the arteries was devised by Chauveau, of the 

 Veterinary School at Lyons. 1 This will give, by calcula- 

 tion, the actual rapidity of the circulation ; and, what is more 

 interesting, it marks accurately the rapid variations in velo- 

 city, with reference to the heart's action. 



The instrument to be applied to the carotid of the 

 horse consists of a thin brass tube, about 1J inch in length, 

 and of the diameter of the artery (about f of an inch), which is 



1 MM. A. CHAUVEAU, G. BERTOLUS et L. LAROYENNE, Vitesse de la Circulation 

 dans Ics Arteres du Cheval. Journal de la Physiologic, Paris, 1860, tome iii., 

 p. 695. 



