232 PHYSIOLOGICAL PHYSICS. [Chap. xxi. 



permitted by the disc 5 5', 1 may be put in communi- 

 cation with 9, and 2 with 8. Suppose the stromuhr 

 be applied to an artery, so that the proximal end is 

 bound to the canule 8 in communication with 1, and 

 the distal end bound to 9. 1 is filled with pure olive 

 oil, 2 with defibrinated blood. On communication 

 being made with the artery, the blood rushes through 

 8 into 1, and forces the oil into 2, and the defibrinated 

 blood from 2 into the artery ; as soon as the blood 

 reaches to the mark 3, the stromuhr is quickly turned, 

 so as to bring 2, now filled with oil, over 8, and 1, 

 filled with blood, over 9. The blood is thus permitted 

 to pass 011 wholly into the artery, and the operation is 

 repeated, 2 becoming in turn filled with blood, and 1 

 with oil, when the instrument is again turned. The 

 number of turns are noted, the time taken, and the 

 capacity of the flasks is known, so that the quantity 

 of blood passing in a given time is ascertained. To 

 tubes projecting from the wall of the tubes 8 and 9 

 manometers can be connected to give the pressure at 

 the entrance and exit of the blood. 



The lisemotacliometer of Yierordt, devised later 

 than Yolkmann's instrument, but earlier than Lud- 

 wig's, affords another means of estima- 

 ting the velocity of the current. It is 

 formed of a metal chamber (Fig. 110), 

 with plain glass sides. Projecting from 

 each end is a canule, a and b. In the 

 chamber hangs a small pendulum. At- 

 no. Vier- tached to one side is a scale, in the form 

 tachometer!" of an arc, for reading off the deviations 

 of the pendulum. The instrument is gra- 

 duated by forcing water through the chamber, and noting 

 the deviation of the pendulum with different veloci- 

 ties. It is then inserted in the course of a vessel, and the 

 rapidity of the current estimated by the deviation of the 

 pendulum interpreted by the prepared table of values. 



