THE MAIN FACTS OF THE CIRCULATION. 



153 



[FiG. 47. 



posing that the quantity held by the bulb A when filled up to the mark x is 5 c.c., 

 and supposing that from the moment of allowing the first 5 c.c. of blood to begin 

 to enter the tube to the moment when the escape of the last 5 c.c. from the artery 

 into the tube was complete, 100 seconds had elapsed, during which time 5 c.c. 

 has been received ten times into the tube from the artery (all but the last 5 c.c. 

 being returned into the distal portion of the artery), obviously 0.5 c.c. of blood 

 had flowed from the proximal section of the artery in one second. Hence, sup- 

 posing that the diameter of the canula (arid of the artery, they being the same) 

 were 2 mm., with area therefore of 3.14 square mm., an outflow through the sec- 

 tion of 0.5 c.c. or 500 mm. in a second would give (-|~) a velocity of about 159 

 mm. in a second. 



The hgematachometer of Vierordt [Fig. 47] is constructed on the principle of 

 measuring the velocity of the current by observing the amount of deviation under- 

 gone by a pendulum, the free end of which hangs loosely in the stream. A square 

 or rectangular chamber, one side of which is of glass 

 and marked with a graduated scale in the form of an 

 arc of a circle, is connected by means of two short 

 tubes with the two cut ends of an artery ; the blood 

 consequently flows from the proximal (central) por- 

 tion of the artery through the chamber into the distal 

 portion of the artery. Within the chamber and sus- 

 pended from its roof is a short pendulum, which when 

 the blood-stream is cut off from the chamber hangs 

 motionless in a vertical position, but when the blood 

 is allowed to flow through the chamber, is driven by 

 the force of the current out of its position of rest. The 

 pendulum is so placed that a marker attached to its free end travels close to the 

 inner surface of the glass side along the arc of the graduated side. Hence the 

 amount of deviation from a vertical position may easily be read off on the scale 

 from the outside. The graduation of the scale having been carried out by experi- 

 menting with streams of known velocity, the velocity can at once be calculated from 

 the amount of deviation. 



An instrument based on the same principle has been invented by Chauveau and 

 improved by Lortet, Fig. 48. In this the part which corresponds to the pendulum 



FIG. 48. 



Hsematachometer of Vierordt 

 a, b, mouthpieces.] 



Hsematachometer of Chauveau and Lortet. 



in Vierordt' s instrument is prolonged outside the chamber, and thus the portion 

 within the chamber is made to form the short arm of a lever, the fulcrum of which 

 is at the point where the wall of the chamber is traversed, and the long arm of 

 which projects outside. A somewhat wide tube, the wall of which is at one point 



