406 THE MECHANICS OF THE CIRCULATION, HEMODYNAMICS 



rests upon a millimeter scale. As the blood strikes its lower end, it is 

 deflected in the direction of the current, its degree of deflection being 

 clearly marked upon the scale. Naturally, this apparatus is first 

 graduated with currents of water of known velocity. It can also be 

 made to register its deflection by simply attaching the long arm of the 

 pendulum to the membrane of a tambour. 



The speed of the flow in the arteries and veins may also be de- 

 termined with the help of the stromuhr which, as has been stated above, 

 measures the quantity of blood traversing a 

 blood-vessel in a given period of time. This 

 calculation, however, also necessitates the de- 

 termination of the internal diameter of this 

 vessel. Burton-Opitz^ and Tschuewsky^ have 

 made use of the following simple procedure 

 in obtaining this value. Having ascertained 

 the external diameter by means of calipers, 

 the blood-vessel was gently compressed be- 

 tween two thin platelets of glass until it be- 

 came empty. The thickness of the platelets 

 and vessel wall was then subtracted from 

 the external diameter, and in addition also 

 the thickness of the platelets. The fact that 

 the speed in the arteries is astonishingly 

 great has been brought out by the experi- 

 ments of Volkmann, Dogiel and Chauveau. 

 The maximal speed in the carotid artery of the 

 dog is given as 500 mm. in a second during 

 systole and as 250 mm. during diastole. In 

 the horse, the speed varies between 520 mm. 

 and 150 mm. in a second, and naturally, these 

 systoHc-diastolic differences are most evident 

 in the arteries in the immediate vicinity of 

 the heart. In the smaller arteries the flow is 

 quite constant. The same holds true of the 

 capillary flow although it may be rendered 

 remittent at any time by producing a slight obstruction centrally to 

 the capillary area. Burton-Opitz and Tschuewsky have furnished 

 the following average values: 



Carotid artery 241,0 mm. in a second 



Femoral artery 234 . 4 mm. in a second 



Hepatic artery 350. mm. in a second 



In general, therefore, it may be said that the velocity of the blood 

 flow in the peripheral arteries amounts to 250-300 mm. in a second. 

 It decreases somewhat in the smaller arteries, reaching its minimum 



1 Am. Jour, of Physiol., vii, 1902, 435. 



2 pfliiger's Archiv, xcvii, 1903, 286. 



Fig. 220.— The Hemo- 



DROMOGRAPH OF ChAUVEAU 

 AND LORTET. 



B, blood-vessel. The 

 end of the pendulum (P) 

 is played against by the 

 blood, its deflection being 

 registered by the receiving 

 drum (T) which in turn is 

 connected with a recording 

 tambour (Jf^). The pendu- 

 lum is contained in a cannula 

 (M).. 



