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The Viscosity of the Blood. 



By A. du Pre Denning, M.Sc. (Birm.), B.Sc. (Lond.), Ph.D. (Heid.), and 

 John H. Watson, M.B., B.S. (Lond.), F.E.C.S. (Eng.). 



(Communicated by Professor Gotch, F.E.S. Eeceived May 7, — Eead May 31, 



1906.) 



The full importance of a knowledge of the variations in the viscous 

 resistance to be overcome by the blood in circulating through the capillaries 

 and smaller vessels, and the actual significance of such data to the more 

 thorough consideration of a large number of normal and pathological con- 

 ditions, especially those of the circulatory system, has perhaps never been 

 fully realised or appreciated either by physiologists or by clinicians in this 

 country. 



Although the subject of the viscosity of the blood has from time to time 

 during the last 60 years attracted the attention of a few well-known investi- 

 gators, yet, so far as we know, there has been no serious attempt to apply 

 systematically the results of their researches to either the theory or practice 

 of medicine. 



The possibility of such investigations proving factors of consequence in 

 certain physiological and pathological states has been strongly emphasised 

 by Professor Osier in the ' American Journal of the Medical Sciences,' 

 writing on the subject of chronic cyanosis with polycythemia. " It is 

 especially important to test the viscosity of the blood by accurate physical 

 methods, and to determine the relation of the number of corpuscles to the 

 viscosity." 



But before entering into any details of the present series of experiments, 

 it may be well to give here a simple interpretation of the term viscosity. 



When a liquid is flowing steadily through a tube or pipe, the layers of the 

 fluid immediately next to the walls of the containing channel are practically 

 at rest, and consequently act as a drag upon the more rapidly moving layers 

 nearer the central stream. Now the force exerted by the sum total of these 

 " drags," or shears, that is, the viscous resistance offered to the fluid motion, is 

 different for different liquids. Or we may say briefly that the viscosity of a 

 liquid is that property whereby it resists the relative motion of its constituent 

 parts. 



Historical. 



From experiments upon the flow of distilled water through capillary glass 

 tubes placed horizontally, Poiseuille, in 1843, obtained data which find full 

 expression in the well-known formula — 



