CH. XXL] 



THE STROMUHR 



279 



that the blood can flow straight across from one section of the artery 

 to the other ; then at a given instant it is turned into the position 

 shown in the diagram, and the blood has to traverse the long (J -tube, 

 and the time that it takes to traverse the tube, the length of which 

 is known, is accurately observed. If the sectional area of the tube is 

 the same as that of the artery, the velocity is obtained without 

 further correction; but the difficulty of obtaining glass tubes with 

 the exact calibre of every blood-vessel which one desires to experi- 

 ment with led to the abandonment of this method, and Ludwig's 

 Stromuhr (literally stream-clock) took its place. This consists of a 

 (J -shaped glass tube dilated at a and a', the ends of which, h and i, 



hllliWuWil 



FIG. 279. Volkmann's 

 Hsemodromomtter. 



Fio. 280. Ludwig's 

 Stromuhr. 



are of known calibre. The bulbs can be filled by a common opening 

 at k. The instrument is so contrived that at & and V, the glass part 

 is firmly fixed into metal cylinders, attached to a circular horizontal 

 table c c, capable of horizontal movement on a similar table d d, 

 about the vertical axis marked in the figure by a dotted line. The 

 openings in c c', when the instrument is in position, as in fig. 280, 

 corresponds exactly with those in d d' ; but if c c is turned at right 

 angles to its present position, there is no communication between h 

 and a and i and a, but li communicates directly with i ; and if turned 

 through two right angles c communicates with d, and c with d', and 

 there is no direct communication between h and i. The experiment 

 is performed in the following way : The artery to be investigated 



