172 MEASUREMENT OF THE VELOCITY OF THE BLOOD-CURRENT. 



blood-vessel; nevertheless the blood is said not to flow more rapidly through it 

 than through the larger, uninjured blood-vessel. The intercalation of the tube 

 offers additional resistance to the blood-current, in consequence of which increased 

 retardation must be produced. The apparatus is evidently imperfect; for the 

 larger respiratory and pulsatory variations of pressure in the arterial system do not 

 produce any perceptible changes in pressure. 



i 



FIG. 68. A. A. W. Volkmann's Hemodromometer. B. C. Ludwig's Rheometer. 



2. Carl Ludwig's rkeometer measures the velocity of the blood-stream from 

 the amount of blood that passes from the artery into a communicating graduated 

 glass bulb. 



Two communicating glass bulbs (Fig. 68, B, A and B), of the same capacity 

 and accurately graduated, are attached by their lower extremities to metallic discs 

 e 6j by means of tubes c and d. Each disc can be turned about the axis x y in such 

 a way that after it has been turned the tube c communicates with f and the tube 

 d with g; f and g are, in addition, provided with horizontal cannulae h and k, 

 which are tied into the extremities of the divided artery. When the instrument 



