viii BLOOD-STKEAM : MOVEMENT IN VESSELS 283 



Vierordt's many observations. When, further, we compare the 

 time of circulation with the number of heart-beats required to 

 complete it, we arrive, according to Vierordt's experimental data, 

 at the fact that twenty-six to twenty-nine pulsations are necessary 

 in every animal, independent of the mass of its body, to drive the 

 blood through the whole circulation from one jugular to the other. 

 This is seen from the following table : 



As regards the time of the circulation in man, Vierordt thinks 

 it probably stands midway between that of the dog and the horse, 

 i.e. he estimates it = 27'1 sees., which with a pulse-frequency of 72 

 per minute corresponds to 27'7 heart-beats. 



These data for the circulation time obtained by the methods of 

 Hering and Vierordt express not the mean velocity with which 

 the blood circulates in the vessels, but rather the maximal 

 velocity, i.e. that of the axial lines of the fluid flowing through the 

 vessels (see p. 189). V. Kries (1887) accordingly proposed to 

 reduce Vierordt's figures by half, to obtain the value of the average 

 velocity of the circulation. By the laws of hydrodynamics, the 

 mean velocity of a fluid traversing a tube must be equal to half 

 the greatest velocity of the axial current. Tigerstedt, however, 

 pointed out that the theory of the passage of fluids was only 

 applicable to the capillaries on the assumption that the stream of 

 fluid is free from solid particles, which depress the value of the 

 maximal velocity in the axial current. We know that the 

 erythrocytes which move in the axial current are so large that 

 they almost fill the capillary lumen, hence the mean velocity 

 in the blood capillaries must certainly be somewhat more than 

 half the maximal velocity. Still it can be positively affirmed that 

 the average time of circulation must be less than that given by 



Bering's method. 



BIBLIOGRAPHY 



In addition to Bibliography at the end of Chap. VII. (p. 231) see : 

 E. H. u. W. WEBEII. Wellenlehre auf Versuche gegriindet. Leipzig, 1825. 



Observations anat. et phys. Lipsiae, 1825. Ber. d. sachs. Gesell. d. 



"Wissenschaften, 1850. Arch. f. Anat. und Physiol., 1851-1853. 

 VOLKMAXN. Die Hamodynaniik. Leipzig, 1850. 

 DONDERS. Physiologic des Menschen. Leipzig, 1859. 

 A. FICK. Medicinische Physik. 2nd ed. Braunschweig, 1866. 

 LANDOIS. Lehre voni Arterienpuls. Berlin, 1872. 



