188 EXPERIMENTAL PHYSIOLOGY 



displaced and the blood previously entering a is sent into the peripheral end 

 of the vessel. When b becomes full the apparatus is again rapidly rotated, 

 and the operation repeated several times, when the experiment is stopped 

 and the total time occupied observed. 



If now we know, by previous measurement, the capacity of the 

 bulbs and the number of times they have been rotated, we know the 

 total volume of blood that has left the artery during the experiment. 

 Suppose this to be V c.c, and the whole time of the experiment to be 

 t seconds. Then in 1 sec. a volume of Y/t c.c. left the artery. The 

 lumen of the artery is next measured. Suppose this to be a sq. cm., 

 and that the velocity of the blood is v cm. per sec. Then the volume 

 of blood leaving the vessel in 1 sec. would be a . v c.c. 



Hence a.v = Y/t, 



and v= — . 



a . t 



Thus from a measurement of the area a of the lumen of the vessel, 

 and the volume V issuing in a time t, we can, by the above formula, 

 determine v, the velocity of the blood flow, along the artery. 



