THE CIRCULATION OF THE BLOOD AND LYMPH in 



filled with oil, and the other with defibrinated blood. The limb con- 

 taining the oil is first put into communication with the central end, 

 and that containing the blood with the peripheral end of the artery. 

 The blood from the artery rushes in and displaces the oil into the 

 other limb, the defibrinated blood passing on into the circulation. As 

 soon as the blood has reached a certain height, indicated by a mark, 

 the instrument is reversed, and the oil is again displaced into the 

 limb it originally occupied. This process is repeated again and again, 

 the time from beginning to end of an experiment being carefully 

 noted. The number of times the blood has filled a bulb in that 

 period, the capacity of the bulb and the cross-section of the vessel 

 being known, all the data required for calculating the velocity of the 

 blood in the vessel have been obtained. 



Suppose, for example, that the capacity of the bulb up to the mark 

 is 5 c.c., and that it is filled twelve times in a minute, the quantity 

 flowing through the cross-section of the artery is i c.c., or i ,000 cub. 

 mm. per second Let the diameter of the vessel be 3 mm., then its 



sectional area is TTX (-) = - = 7-06 sq. mm. The velocity is 



= 141 mm. per second. 



1000 



7*06 



Various improvements in this method have been made, such as 

 graphic registration of the reversals of the stromuhr. 



3. A tube or box, in which swings a small pendulum, is inserted 

 in the course of the vessel. The pendulum is deflected by the blood, 

 and the amount of the deflection bears a relation to the velocity 

 of the stream (Vierordt's hczmatachometer ; Chauveau and Lortet's 

 much more perfect dromograpti) (Fig. 33). 



4. Pitofs Tubes. If two vertical tubes, a and b, of the form 

 shown in Fig. 32, be inserted into a horizontal tube in which liquid 

 is flowing in the direction of the arrow, the level will be higher in a 

 than would be the case in an ordinary side-tube without an elbow ; 

 in b it will be lower. For the moving liquid will exert a push on the 

 column in a, and a pull on that in b. The amount of this push and 

 pull will vary with the velocity, so that a change in the latter will 

 correspond to an alteration in the difference of level in the two tubes. 

 Instruments on this principle have been constructed by Marey and 

 Cybulski, the former registering the movements of the two columns 

 of blood by connecting the tubes to tambours provided with writing 

 levers, the latter by photography (Fig. 36). 



5. The electrical method, described on p. 123, for the measurement 

 of the circulation time, can also be applied to the estimation of the 

 mean velocity of the blood between two cross-sections of the arterial 

 path which are separated by a sufficient distance. For example, salt 

 solution can be injected into the left ventricle or the beginning of 

 the aorta, and the interval which it takes to reach a pair of electrodes 

 in contact with, say, the femoral artery, determined. Knowing the 

 distance between the point of injection and the electrodes, we can 

 then calculate the mean velocity. 



