THE BLOOD 233 



ions in equal degree and therefore are neither acid nor alkaline but neutral 

 in reaction. 



6. Temperature. The temperature varies in degree in different parts 

 of the body. If the temperature variations correspond with the variations 

 in some other mammals, the highest temperature is in the hepatic veins 

 where, as in the dog, it registers about 4o.6C., and the lowest temperature 

 is near the surface as in the mouth and axilla, where it is approximately 

 38. 9 C. 



7. Viscosity. Viscosity may be denned as the resistance to the move- 

 ment of the molecules of a fluid homogeneous body among themselves. In 

 accordance with the degree of this resistance, which may also be spoken of 

 as internal friction, will the fluid at a given temperature be mobile or viscous. 

 Viscosity varies partly with the nature of the fluid and partly on its tempera- 

 ture. Thus at the same temperature water, syrup, and pitch possess different 

 degrees of viscosity. A rise in temperature of iC. diminishes the viscosity 

 about 2 per cent. In all discussions relating to the viscosity of fluids, that 

 of distilled water is taken as a standard and regarded as unity. 



Blood as a fluid is regarded by physiologists as possessing viscosity, 

 though the definition in the foregoing paragraph is not strictly applicable, 

 as it is not a homogeneous but a heterogeneous fluid consisting of plasma 

 the molecules of which show an inner friction and of corpuscles, which also 

 show friction. Blood having a complex composition as compared with 

 water has naturally a greater degree of viscosity or internal friction. Experi- 

 mental investigations render it certain that the observed viscosity is depend- 

 ent on the corpuscular elements to a greater extent than on the composition 

 of the plasma. About two-thirds of the viscosity is due to the corpuscles. 



The viscosity of blood as compared with water may be determined by 

 permitting the two fluids to flow through capillary tubes of corresponding 

 caliber under a steadily acting pressure and then determining the volume 

 that flows through each in a given time, or by determining the distance to 

 which each fluid flows in a unit of time 'in these capillary tubes and then 

 in each instance, comparing the results one with the other. Normal human 

 blood is thus found to possess a viscosity 4.5 times that of distilled water 

 at body temperature. Dog's blood has- a viscosity 6 times that of water. 

 If the temperature of blood is raised the viscosity diminishes. Recalling 

 the statement that the viscosity is closely connected with the presence of 

 red corpuscles it would be expected that either an increase or decrease 

 in their number would change the viscosity in one direction or another. 

 In a case of polycythemia in which the red corpuscle count was 11,000,000 

 per cubic millimeter the viscosity was between 3 and 4 times the normal. 

 In certain other pathologic states of the blood characterized by a diminu- 

 tion in the number of red corpuscles the viscosity diminished one-half 

 or more. The ingestion of meat raises the viscosity, while the ingestion of 

 fats and carbohydrates diminishes it. 



The determination of the viscosity for clinical purposes is accomplished 

 by the use of special forms of apparatus termed viscosimeters. These for 

 the most part consist of capillary tubes through which distilled water and 

 blood are caused to flow under the influence of a constant positive or nega- 

 tive pressure. The distance the water flows in a unit of time, compared 

 with that of blood, represents the degree of viscosity. Among these ap- 



