1002 



PHYSIOLOGY 



Cybulski's photohaematachometer. The hcemadromograph (Fig. 385) consists 

 of a pendulum which is hung in a tube, through which the blood is allowed to 

 flow, placed in the course of the artery. The deviation of this pendulum from 

 the vertical will be in proportion to the velocity of the current, and if its upper 

 end be connected, as in the diagram, with a tambour, the variations in velocity 

 can be recorded on a blackened surface by means of a lever. The photohcemata- 

 chometer is based on an interesting application of Pitot's tubes. If a current of 

 blood be directed along the tube ab possessing two vertical side tubes c and d 

 (Fig. 386), the pressure at c will be greater than that at d, since at c the momentum 



m 



n 



J 



pi 



FIG. 385. Diagram showing the 

 construction of Chauveau's 

 haemr dromograph. 



FIG. 386. Diagram to show principle of 

 construction of Cybulski's photo-hsemata- 

 chometer. 



of the moving mass of blood is added to the lateral pressure of the fluid. A tube 

 of this shape is connected with an artery, such as the carotid, and the tubes 

 h and h' are attached at the points c and d. These two tubes are united at their 

 upper extremities. In this case so long as the blood flows from a to b the fluid 

 in h will rise higher than in h' t and the difference in height of the fluid in the 

 two tubes will be proportional to the velocity of the blood. A graphic record of 

 this difference of pressure is obtained by allowing a narrow beam of light to throw 

 an image of the menisci of the two columns of fluid through a slit on to a moving 

 photographic plate. Such a record is given in Fig. 387. The width of the black 

 space at any point is proportional to the velocity of the blood at the moment 

 at which this part of the record was being taken. Of course this instrument has 

 to be calibrated if we wish to determine the velocity of the blood in absolute 

 measure. In Fig. 387 the velocity at the points 1 and 1", corresponding to the 

 cardiac systole, was 248 mm. per second. At 2 and 2', corresponding to the 



