ADVANCED DEMONSTRATIONS 



391 



valves close at the beginning of the dicrotic notch (4). The period of 

 rising tension lasts from the beginning of systole (1) to the opening 

 of the semilunar valves (2). 



Velocity of Blood Flow. Insert the Pitot tubes E and F into 

 a tube A through which water is flowing from a constant head of 

 pressure B (Fig. 253). Note that the water 

 rises to different levels in the tubes. E re- 

 cords the resistance head plus the velocity 

 head. F records the resistance head minus 

 the velocity head. Measure the outflow per 

 minute from the tube A, and note the difference 

 between the heights of the menisci in E and 

 F. Lessen the velocity by partly screwing 

 up the clip on the end A. Measure the out- 

 flow per minute, and note that the menisci 

 are nearer together. Close the end of A. The 

 flow ceases, and the menisci in the two tubes 

 reach the same level as that of the head of 

 pressure B. Cybulski makes use of this 

 principle in the construction of the photo- 

 haematochometer, an instrument by which 

 alterations in velocity can be recorded 

 Fig. 253. 



The velocity can also be measured in the 

 artificial schema by injecting 1 c.c. of methy- 

 lene blue sat. sol. into artery, and noting 

 by means of a stop-watch (or electric signal and drum) the moment of 

 injection, and the moment when the blue fluid reaches the capillary tube. 



The Circulation Time. In the artificial schema measure the circu- 

 lation time by injecting methylene blue into the vein V, and noting 

 how long the blue takes to reach the venous end of the capillary tube. 



FIG. 253. Cybuiski's photo- 

 haematochometer. A cannula 

 shaped as shown is introduced 

 into the blood-vessel. The os- 

 cillations of the mercury-menisci 

 are photographed. 



CHAPTER XL. 

 THE WORK OF THE HEART. THE PERICARDIUM. 



The Work of the Heart. To estimate the work of the heart in the 

 artificial schema the mean pressure H, and velocity in the aorta V, and 

 the volume of the systolic output Q, must be obtained. 





