180 MEASUREMENT OF THE VELOCITY OF THE BLOOD-STREAM. 



with salt solution]. The stop-cocks are moved simultaneously, as they are 



attached to a toothed wheel and have at first the position given in Fig. 81, I, 



so that the blood simply flows through the hole in the v 



basal piece, i.e., directly from one end of the artery to 



the other. If at a given moment the stop-cock is 



turned in the direction indicated in Fig. 81, II, the 



blood has to pass through the glass tube, and the time 



it takes to make the circuit is noted, and as the length 



of the tube is known, we can easily calculate the velocity 



of the blood. 



Volkmann found the velocity to be in the 

 carotid (dog) = 205 357 mm. ; carotid (horse) = 

 306; maxillary (horse) = 232; metatarsal= 56 

 mm. per second. The method has very obvious 



Fig. 81. 



Volkmann's H^madromometer (B) I, blood 

 flows from artery to artery ; II, blood 

 must pass through the glass tube of 

 B ; c, c, canuula; for the divided artery. 



Y 



Fig. 82. 



Ludwig & Dogiel's Stro- 

 muhr or Rheometer 

 X, Y, axis of rotation ; 

 A, B, glass bulbs ; h, k, 

 cannuloj inserted in the 

 divided artery; e,e\, ro- 

 tates on g, f; c, d, tubes. 



defects arising from the narrowness of the tube; the introduction of 

 such a tube offers new resistance, while there are no respiratory or pulse 

 variations observable in the stream in the glass tube. 



