MEASUREMENT OF THE VELOCITY OF THE BLOOD-CURRENT. 



is in the position shown in the figure, h is tied in the central, and k in the peripheral 

 extremity of the vessel (for example, the carotid). The bulb A is filled with oil 

 and the bulb B with defibrinated blood. At a given moment the blood-current 

 is permitted to enter through h ; the oil is displaced by the blood and passes over 

 into B, while the defibrinated blood flows out from B through k into the peripheral 

 portion of the vessel. As soon as the oil reaches m, the time is again noted, and 

 the entire apparatus A B is turned about the axis x y, so that B occupies the place 

 of A. The phenomenon is thus repeated, and the observation may often be con- 

 tinued for some time. By observing the time required by the inpouring blood 

 to fill one of the bulbs the quantity for each unit of time (second) can be cal- 

 culated. 



3. Carl Vierordt's hemotachometer measures the velocity of the blood-cur- 

 rent by means of a device modeled after Eitelwein's velocity- quadrant, which 

 is constructed on the principle that a pendulum suspended in a moving fluid is 

 deflected by the current in proportion to the velocity. 



The apparatus consists of a small metallic box (Fig. 69, I. A) with parallel 

 glass sides and provided at the narrow extremities with two cannulae (e, a) for the 



. iG. 69. Vierordt's Hemotachometer: II, Chauveau's and Lortet's dromograph; III, the dromographic curve 



according to Chauveau. 



entrance and exit of the blood. Within the box, opposite the entering blood- 

 current, hangs a small pendulum (p) , the oscillations of which are read off on a 

 curvilinear scale and which increase with the velocity of the current. Before 

 making an observation, water is allowed to flow through the instrument for the 

 purpose of determining the velocity of the fluid that corresponds to each degree 

 of deviation of the pendulum. 



4. Chauveau's and Lortet's dromograph is constructed on the same principle, 

 and is in addition provided with a recording contrivance. 



A sufficiently wide tube (Fig. 69, II, A B), provided with a lateral tube C, 

 which can be connected with a manometer, is introduced into the divided artery 

 (carotid of the horse) . At a there is a small linear opening closed with a rubber 

 plate through which a light pendulum a b projects into the tube. The pendulum 

 is prolonged upward as a thin indicator (b), which makes excursions proportional 

 to the velocity of the current, and which can be read off on the scale S S. G repre- 

 sents a handle for fixing the instrument. The apparatus is first tested with water 

 to determine the excursions corresponding to the various velocities. As the 

 indicating pendulum is exceedingly light it records the slightest changes in velocity. 



