v THE BLOOD: PLASMA 151 



the viscosity of blood plasma, to which no one had called attention 

 previous to the interesting work of Albanese, On the Influence of 

 the Composition of Nutritive Fluids on the Activity of the Isolated 

 Frog's Heart (1893). 



Let it be said in the first place that the viscosity of a homo- 

 geneous fluid, such as plasma or blood serum, is due to the internal 

 friction between its molecules and those of the solvent (water), 

 and of the bodies in solution or in pseudo-solution (colloids), 

 whether or no these are electrolytes, dissociated or non-dissociated ; 

 and that in heterogeneous fluids, such as the blood, entire or defi- 

 brinated, the viscosity is largely augmented by the presence of the 

 corpuscular elements. 



It varies considerably with temperature, and is measured by 

 special instruments called viscometers. The measurement is based 

 on the time which a known volume of fluid takes to pass along a 

 capillary tube. When the pressure under which the fluid passes, 

 and the dimensions of the capillary tube, are known, it is possible 

 to obtain absolute values (/>) of viscosity ; but often it suffices 

 to obtain the relative value (17) by comparison with that of another 

 fluid, e.g. distilled water. 



Hlirthle suggested another method by which it is possible to 

 determine the viscosity of circulating blood in the living animal ; 

 but better results are obtained experimentally in vitro and with 

 blood serum. 



Bottazzi found the value 77 at 15 C. for dog's serum = 2-0233- 

 2-0486, and at 39 C. = 1-84-1-87 ; Mayer at 40 C. for mammalia 

 obtained values that oscillated between 1*41 and 1-95. In the dog 

 the viscosity of serum and defibrinated blood is as 1 : 5 (Bottazzi). 



The viscosity of blood determined by Albanese with Ostwald's 

 viscometer (v. Grundriss der allgemeinen Chemie, Leipzig, 1890) is 

 approximately equal to that of a 2-3 per cent solution of gum 

 arabic. He believes in a certain constant ratio between isotonicity 

 and isoviscosity ; but this seems improbable, since the fluids within 

 the body are isotonic but not isoviscous. 



The physiological importance of viscosity depends principally 

 on the great resistance which it entails on the blood passing 

 through the capillaries, and on the corresponding effort that must 

 be made by the heart. But it is probable that the high viscosity 

 of the blood and the presence of colloids influence some chemical 

 reactions in a way that does not obtain in pure water or in fluids 

 of less viscosity ; and this notwithstanding that the diffusion of 

 crystalloids in colloid solutions is effected with the same rapidity 

 as in water. From this it appears that a fluid, in order to be 

 completely physiological, that is to say, indifferent and innocuous 

 to the living tissues, must, besides being isotonic and isoconductive, 

 be also isoviscous, i.e. it must possess a degree of viscosity equal to 

 that of blood plasma. 



