The Viscosity of the Blood. 



329 



V ~ 81Q ' 



where tj = the viscosity coefficient, 

 p—p' = the pressure gradient, 



r = the radius of the capillary bore, 

 I = the length of the tube, 

 Q = the quantity of liquid flowing between 

 two fixed marks in the time t* 



This law has been found to hold with great exactness not only for water, 

 but for most homogeneous solutions. But when Poiseuille, and at a some- 

 what later date Eegnault, examined the rate of flow of blood through a 

 Poiseuille viscosimeter, they met with marked irregularities which they 

 felt bound to ascribe to variations in the composition of the blood. 



Except for Donders' reference to Poiseuille's results during the course of a 

 discussion on heemo-dynamics between Volkmann and Weber, these deter- 

 minations of the blood viscosity were for many years practically ignored, 

 probably owing to difficulties caused by coagulation. True, in ' Ludwig's 

 Text-Book of Physiology,' published in 1861, we find references to the work 

 of Poiseuille, Darcy, Dubuat, and Girard, and a statement to the effect that 

 " die Geschwindigkeit veranderlich ist mit der Zusammensetzung der 

 Fliissigkeit." 



In this country, in 1874, Duncan and Gamgee made some experiments on 

 the rate of flow of blood through tubes of narrow diameter, and observed 

 that the rate of flow of blood taken directly from the vessels of a living 

 animal is very much greater than that of defibrinated blood. This they 

 explained by assuming that in the defibrinated blood there is a tendency for 

 the blood corpuscles to run together and form small corpuscular masses or 

 clumps, which would tend greatly to diminish the rate of flow of the liquid 

 column in which they were suspended, and so might probably give rise to 

 the observed deviations from Poiseuille's law.t 



Ewald, working with defibrinated blood in 1877, found a value for its 

 viscosity, which was about five times that of water.J 



A similar result was obtained in 1896 by Mcolls, who used a modified form 

 of Poiseuille's viscosimeter ;§ whilst Lewy, also working with defibrinated 

 blood, gave its value as times that of water.|| 



* Poiseuille, 'Ann. d. Chim. et de Phys.,' 3 ser., vol. 1, p. 21, 1847. 



t Duncan and Gamgee, ' Journ. Anat. and Physiol.,' vol. 5, p. 184, 1874. 



\ Ewald, « Arch. f. Physiol.,' Leipzig, 1877. 



§ Nicolls, ' Journ. Physiol.,' vol. 20, p. 407, 1896. 



|| Lewy, 'Arch. Physiol.,' vol. 70, Bonn, 1897. 



