THE CIRCULATION OF THE BLOOD 361 



Since neither the blood nor any particle placed in it can be seen through the 

 walls of the artery, it occurred to Volkmann to intercalate along the course 

 of a vessel a U-shaped glass tube about one meter in length with a lumen 

 the diameter of that of the selected vessel, into and through which the 

 blood could be made to flow. The mechanic construction of the apparatus 

 is such (Fig. 167) that the blood can be made to flow directly into the distal 

 portion of the artery across the base or indirectly 

 by way of the glass tube. Previous to the inter- ;; 



calation of the tube it is filled with serum or nor- 

 mal saline solution. With the turning of the cocks 

 as B the blood enters the glass tube and drives the 

 serum ahead of it into the arterial system. From 

 the difference in time between the moment the 

 blood enters and the moment it leaves the tube and 

 from the capacity of the tube the velocity is 

 determined. 



The Stromuhr or rheometer of Ludwig (Fig. 168) 

 is constructed on the same principle, but instead of 

 the glass tube having the same diameter it is 



FIG. 167. VOLKMANN' s HEMODROMOME 

 TER. C, C. Arterial cannulas. 



FIG. 1 6 8 LUDWIG AND 

 DOGIEL'S RHEOMETER. X . V. 

 Axis of rotation. A, B. Glass 

 bulbs. h,k. Cannulas inserted 

 in the divided artery. f,ti, 

 rotates on g, /. c, d. Tubes. 





