IV. V I S C O S I T Y M E A S U R E M E N T S 125 



E. RESULTS OBTAINED FROM VISCOSITY STUDY 



Numerous authors have studied the viscosity of the blood of vari- 

 ous mammals. Essentially the same values have been obtained for 

 the past forty or fifty years. Ordinarily, in recent studies at least, 

 the Hess viscometer is used. With this apparatus, as noted pre- 

 viously, measurements can be made at various pressures, but usually 

 only a single pressure is used, and the viscosity of the blood at this 

 pressure is compared with the viscosity of water. 



Blood plasma and blood serum obey Poiseuille's law, but whole 

 blood, to some extent, shows an anomalous viscosity. The variation 

 from Poiseuille's law only becomes significant for very low shearing 

 forces; this variation tends to become more evident if the capillary 

 tube through which the blood flows has a small diameter (see Hess, 

 26). In making comparisons of the rheological properties of various 

 tjrpes of bloods, Bingham and Roepke (27) prefer to use the fluidity 

 value instead of the viscosity value. The fluidity is the inverse of 

 the viscosity, and its unit, the rhe, is l/rj. Recent data on the vis- 

 cosity of the blood of various mammals and birds are given by Rhiel 

 (28) and Moll (29). 



In clinical diagnosis the viscosity of the blood is sometimes meas- 

 ured, although such measurements are not thought to have as much 

 diagnostic value as the results obtained from the other types of meas- 

 urements. Usually the normal viscosity of the blood (in terms of 

 the viscosity of water) is taken as 4.5. In cases of anemia and nephri- 

 tis, the viscosity is lower, and it is usually lower also in leukemia and 

 malaria. In diabetes mellitus and in jaundice, the viscosity is low, 

 and this is usually true also in pneumonia. In general, although not 

 always, when the volume of red blood cells in a given volume of blood 

 is high, the viscosity of the blood is greater (c/. 30). Under conditions 

 that induce excessive sweating, most of the loss of water is from the 

 blood, and such water loss is accompanied by increased viscosity. 

 In traumatic shock also, there is typically a loss of water from the 

 blood. Such changes in the total blood volume are usually studied 

 by measuring the concentration of a dye injected into the blood 

 stream, by hematocrit studies of the volume of blood corpuscles in a 

 given volume of blood, by blood cell counts, by refractometer meas- 

 urements or by hemoglobin determinations. Physiologists and clini- 

 cians are more accustomed to such techniciues than they are to vis- 

 cosity measurements, so that ordinarily, in physiological experimen- 



