324 



CIRCULATORY SYSTEM. 



reaches only up to the mark e; and the bulb A is filled with oil. 

 The clamps which close the ends of the vessel are now removed, 

 the time being noted, and the blood from a expels the oil in A 

 into B. When A is filled with blood to the point c?, the time is 

 again noted, and the capacity of A, and the caliber of the vessel 

 being known, the velocity of the flow may be calculated. A 

 single measurement would not be sufficient to give results of 

 much value ; but if at the moment the blood reaches d the instru- 

 ment is rotated, the bulb B into which the oil has been driven by 

 the blood will be brought into relation with a, and will be filled 

 with blood from the vessel, as A originally was, the oil being 

 forced into A, and the blood contained in that bulb will be driven 

 on into the vessel 6, thus entering the circulation again. When 

 the oil emerging from the bulb reaches the mark, the time is again 

 noted, and the bulb again rotated ; thus the blood which is meas- 

 ured is always the volume be- 

 tween e and d in A. The time 

 between the rotations is the time 

 occupied in filling the bulb, and 

 this may be recorded on a kymo- 

 graph. 



The Dromograph (Fig. 170). 

 This consists of a metal tube, 

 which is inserted into a divided 

 artery ; in the side of the tube 

 is an opening, closed by rubber, 

 through which a lever passes, 

 one end being inside the vessel, 



FIG. 170. Chauveau's dromograph : 



the other outside, and so ar- 



A, tube connected with blood-vessel f B, ranged that its movements are 



metal cylinder in communication with indicated on a dial. The num- 



A. The upper end of B has a hole in i r> j , T 



the center, which is covered by a mem- ber of graduations corresponding 



brane, ro, through which a lever, (7, to a given Velocity is known by 



- C_ has a small disk, j>, at its lower observing the deflection of the 



end, which projects into the lumen of A, 

 and is deflected in the direction of the 

 blood -stream 

 is registered 



lever when it is inserted into a 

 tube 



communication by the tube E with a flowing at a known rate IS pass- 



tambour Z>, the flexible membrane of 

 which is connected with the lever of 

 the pendulum C. 



ing. 



Various observations have 

 been made on lower animals to 

 determine the velocity of the blood-flow in the arteries. In the 

 dog's carotid it is found to be from 205 mm. to 350 mm. per 

 second ; in the same vessel of a horse, 306 mm. ; and in the 

 metatarsal artery of the horse, 56 mm. When an artery divides, 

 the sectional area of the branches is more than that of the 

 original vessel, and this consequently results in a gradually in- 

 creasing sectional area, and a .corresponding diminution in the 

 velocity of the flow, so that in the smaller artery the speed is 



