THE BLOODVESSELS 



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Several ingenious instruments have been devised for the 

 purpose of measuring the velocity of the blood. One, introduced 

 by Ludwig, known as the stromuhr (Fig. 36), consists of a bulb 

 of known size, and the length of time taken to fill this bulb 

 of known capacity gives the velocity. The dromograph of 

 Chauveau (Fig. 37) is employed for a similar purpose : it consists 

 of a tube placed in the course of the vessel ; within the tube is 

 a plate; the blood streaming 

 past this plate deflects a needle, 

 and the angle of deflection may 

 be expressed in terms of velocity. 



By means of these appliances 

 the following velocities have been 

 obtained in the vessels of the 

 horse : 



Carotid artery : 30 to 40 cm. per 



second (118 to 15- 75 inches). 

 Metatarsal artery : 5*5 cm. per 



second (2-2 inches). 

 Jugular vein : 22 cm. per 



second (8- 85 inches). 



The velocity in the larger vessels 

 is not constant ; it is greatest 

 during systole and less during 

 diastole. Chauveau obtained the 

 following results in the carotid of 

 the horse : 



During systole : 52 cm. per 



second (20-47 inches). 

 Beginning of diastole : 2 r 75 cm. 



per second (8*66 inches). 

 During the pause : 15 cm. per 



second (5*90 inches). 



The mean velocity in the 

 carotid of the dog is 26 5 mm. 

 per second (10 J inches). 



Fig. 37. — Chauveau's Dromograph. 



A, Tube connected with blood- 

 vessel ; B, metal cylinder in com- 

 munication with A. The upper 

 end of B has a hole in the centre, 

 which is covered by a membrane, 

 w, through which a lever, C, passes. 

 C has a small disc, p, at its end, 

 which projects into the lumen of 

 A, and is deflected in the direction 

 of the blood-stream through A. 

 The deflection is registered by 

 a recording tambour connected 

 with the lever C. 



At the end of systole : 

 At the end of diastole 



30* 5 cm. per second (12 inches). 

 215 cm. per second (8£ inches). 



The difference between systolic and diastolic velocities becomes 

 less and less as the small arteries are approached, until finally 

 it disappears. We may say, therefore, that the velocity is more 

 uniform in the small than in the large arteries. 



The velocity of the blood is not as great as at first sight 

 appears. If the stream in the carotid of the horse were never 



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