GENERAL CHARACTERISTICS OF THE BLOOD 167 



internal friction, or viscosity. While frequently used as a synonym 

 for the general term of internal friction, the term viscosity should in 

 reality be restricted to that type of friction which has its origin in the 

 qualitative peculiarity of a fluid. 



It has been shown by Burton-Opitz^ that the viscosity of the 

 blood differs greatly in different animals, but remains rather constant 

 in the same group of animals. When compared with distilled water 

 at 37° C.,2 the viscosity of human blood is found to be 5.1 times greater, 

 while that of dog's blood is 5.0 times greater. The coefficient for 

 cat's blood is 4.1, for rabbit's blood 3.1, and for the blood of the frog 

 and turtle 2.5. It is evident, therefore, that the viscosity increases with 

 the complexity of the blood, and thus, it may also be inferred that the 

 viscous resistance of the plasma or serum is very much less than that 

 of whole blood. In fact, it is possible to establish perfectly normal 

 degrees of viscosity by simply adding definite numbers of washed red 

 cells to clear serum. 



The fact that the viscosity of the blood is subject to variations is 

 shown by the observation that warm baths decrease it, whereas cold 

 baths and exposure of the body to hot air increase it. It is also les- 

 sened by hemorrhage and the injection of small quantities of normal 

 saline solution. Arterial blood is less viscous than venous blood; and 

 hence, if a venous character is imparted to the fornier either by tempo- 

 rarily obstructing the trachea or by permitting the animal to inhale 

 carbon dioxid, its viscous resistance becomes greater than normal. In 

 dyspnea it is increased and also during ether and chloroform narcosis, 

 as well as after the administration of alcohol. It is diminished by 

 starvation and increased by feeding, more especially by the ingestion 

 of proteid material.^ 



1 Pfliiger's Archiv, Ixxxii, 1900; cxii, 1906; and cxix, 1908; also Jour, of Physiol., 

 xxxii, 1904 and 1905; Amer. Jour, of Physiol, vii, 1902; and Jour. Exp. Med., viii, 

 1906. 



2 The coefficient of the viscosity for distilled water at 37° C. has been determined 

 by Poiseuille (Ann. de Chem. et de Phys., Paris, 1843, Sec. 3, p. 7). Its value is 

 4700. 



' For clinical purposes the viscosity of the blood is determined with the help 

 of a simple instrument, known as a viscosimeter. An instrument of this kind was 

 first devised by Burton-Opitz (1903). Modifications have been presented more 

 recently by Hirsch and Beck, Hess and Miinzer, and Bloch. 



