THE BLOOD FLOW 



405 



out difficulty by simply noting the time when the blood enters and 

 leaves its orifices. 



Instruments embodying the principle of PitoVs tubes have been 

 designed by Cybulski.^ Two tubes {d and d') which have been bent 

 at right angles, are inserted in the blood-vessel in such a way that the 

 orifice of one points in the direction of the bload stream and that of 

 the other against it (Fig. 219). The level of the saline solution with 

 which they have previously been filled will then rise in the latter and 



^cS 



I -^ I 



u> or 



m^^m^::^^ 



E\ C 



© ® 



Fig. 219. 



Fig. 218. 



Fig. 218. — Volkmann's Hemodromometer. 



A and B, cannulas for connecting the central and distal ends of the blood-vessel with 

 this instrument. C, short cut through base of instrument; D, U-shaped tube of definite 

 length. The blood may be diverted into the latter at any moment by turning the valves 

 E and F. 

 Fig. 219. — Diagram to Show the Principle of the Cybulski Photo-hem otacho- 



METER. 



fall in the former. The push (d) and the pull (d') which the moving 

 blood exerts upon them must, of course, be directly proportional to 

 the speed of the flow. It need scarcely be mentioned that these varia- 

 tions in the levels of the Hquid {h and h') may be recorded either by 

 means of ordinary tambours connected with the ends of these tubes, 

 or by means of a beam of reflected light. 



The hemotachometer, devised by Chauveau and Lortet,^ is another 

 instrument of this type. It consists of a T-tube made of metal, in 

 which a very delicate pendulum is suspended (Fig. 220). The short 

 arm of the latter projects into the blood stream, while its long arm 



1 Pfiiiger's Archiv, xxxvii, 1885, 382. 



2 jour^ de la Physiol., iii, 1860, 695. 



