CIRCULATION. 



391 



N 



FIG. 102. Diagram of longitudinal sec- 

 tion of Ludwig's "Stromuhr." The ar- 

 rows mark the direction of the blood- 

 stream. For further description see the 

 text. 



latter, the calibre of the vessel. For these reasons any measurement of 

 the average speed of the blood by the above method is only approximately 

 correct. The best instrument for measuring 

 the quantity of blood driven past a point 

 during an experiment is the so-called " strom- 

 uhr" or "rheometer" of Ludwig, a longitu- 

 dinal section of which is given diagrammati- 

 cally in Figure 102. 1 This is essentially a 

 curved tube shaped like the Greek capital 

 letter a. Each end of the tube is tied into 

 one of the two stumps (a and 6) of the divided 

 vessel. These ends of the tube are as nearly 

 as possible of the same calibre as the vessel 

 selected. Each limb of the tube is dilated 

 into a bulb, and the upper part of the tube, 

 including the two bulbs, is of glass ; the lower 

 part of each limb is of metal. At the top, 

 between the bulbs, is an opening for filling 

 the tubes, which can easily be closed when not 

 in use. Each end of the tube is filled with 

 defibrinated blood before being tied into the 

 blood-vessel. In the limb of the tube (B, 

 Fig. 102) which is the farther from the heart if an artery be used, or the 

 nearer to the heart if a vein, the defibrinated blood is made to fill the cavity 

 up to the top of the bulb. In the other limb (A, Fig. 102) the blood fills the 

 tube only up to a mark (e, Fig. 102) near the bottom of the bulb. Through 

 the opening between the bulbs the still vacant space, which includes the whole 

 of the bulb A, is filled with oil, all air being excluded. The opening is then 

 closed. If now the clamps be removed from the blood-vessel, the blood of the 

 animal will enter the tube at a and drive before it the contents of the tube. 

 Thus defibrinated blood from B will be driven into the distal stump of the 

 vessel at 6, and will enter the circulation of the animal. Oil will at the same 

 time be driven over from A to B. The bulb A has upon it two marks, d and 

 e, one near the top of it, the other near the bottom. The instant when the 

 line between the oil and the advancing blood reaches the mark near the top 

 of A is the instant when a volume of blood equal to that of the displaced oil 

 has entered A, past the mark near the bottom of it. The capacity of the tube 

 between the two marks is accurately known. The time required for this 

 space to be filled with the entering blood is measured by the observer. The 

 calibre of the metal tube at a is accurately known, and is assumed to be equal 

 to the calibre of the blood-vessel. From these measurements the average 

 speed of the blood-stream at a is calculated. 



1 J. Dogiel : " Die Ausmessung der stromenden Blutvolumina," Bericlite uber die Verhand- 

 lungen der k. sdchsischen Gesellsehaft der Wissenschaften zu Leipzig, Math.-physische Classe, 1867, 

 p. 200. 



