VELOCITY OF BLOOD IN VASCULAR SYSTEM 1001 



equal size, a and 6, communicating with one another above j their lower ends 



are clamped in the disc c, which is pierced by two openings serving to connect the 

 lower orifices of the bulbs with the tubes t, t, cemented 

 into the lower disc ab. 



An artery such as the carotid, being clamped at its 

 central end and divided, a is inserted into its central 

 end, and 6 into its peripheral cut end. The tube a is 

 filled with oil and b with salt solution or defibrinated 

 blood. On clamping the artery, blood flows into a and 

 drives the contained oil over into b, the contents of b being 

 meanwhile forced into the peripheral end of the artery. 

 When blood has completely filled the bulb a, the two 

 bulbs are reversed, and the blood now entering the artery 

 displaces the oil in 6, and forces the blood which had 

 entered a on into the peripheral end of the artery. 

 Knowing the capacity of the bulbs and the number of 

 times it has been necessary to turn them in the course, 



FIG. 383. Diagram of sav > f one minute, we know also the amount of blood 

 Lud wig's ' Stromuhr.' which has passed across the section of the artery under 



experiment. 

 In order to determine from this volume the velocity of the blood across the 



section, i.e. through the artery, the total 



volume passing in the minute must be 



divided by the cross-section. This will 



give the velocity per minute. Many 



modifications of this apparatus have 



been devised. A simple form of current 



measurer is shown in Fig. 384. The 



whole apparatus is constructed of glass. 



The tube a is connected with the central from Artet 



end of a cut artery, and the tube p 



with the peripheral end. The blood flows 



into B and fills it. As soon as it is full 



and its level rises over the level of the 



bend of the siphon tube s, the blood is 



rapidly siphoned off into c, whence it 



flows along p into the peripheral part 



of the artery. The side tube R is con- 

 nected with a mercury or membrane 



manometer. Every time that B is 



emptied into c a depression is produced 



on the manometer tracing, which thus 



records not only the average pressure 



but also the average velocity of ]the blood 



in the artery. Each instrument has to 



be calibrated in order to know how 



much blood passes from B to c each 



time that siphonage occurs. 



None of these methods give any in- 

 formation of any rapid changes occurring 



in the velocity of the blood, e.g. during 



a single pulse -wave. For this purpose we 



must have recourse to some instrument 



such as Chauveau's haemadromograph or 



FIG. 384. A simple blood-current measurer. 

 (IsHiKAWA and STARLING.) 



