176 Kkpokt S.A.A. Advaxckment of Sciencl:. 



II. THE PHYSICAL LAWS OF LK^L'ID.S. 



T() all these body-liquids the general physical laws of liquids must 

 be ap{ilicable. The most important from our point of view are the 

 following: Every liquid has (1) a characteristic internal friction or 

 viscosity ; (2) a characteristic surface tension. Liquids have no shape 

 of their own, but only such as is caused by external intluences {e.y. form 

 and ishape of the vessel, intluence of the eartli's attraction), but in spite 

 of that the liquids offer a certain resistance to every power which tends 

 to provoke a mo\ement in them, producing internal friction or viscosity. 

 The viscosity is therefore the reciprocal expression of the tiuidity of the 

 liquids. 



{a) Viscosity. 



L'sually the internal friction of H.,0 is taken as = 1 ; compared 

 with water the internal friction oi the above-mentioned fluids of the 

 body is always higher, every one showing a certain constancy and 

 specifity in each species of animal. Viscosity is dependent upon the 

 substances which are dissolved in the liquid (salts) or contained in it 

 as colloidal substances (proteids, enzymes). As soon as we know the 

 intluence of all of these bodies or of certain classes of them alone, the 

 ^■iscosity indicates the presence or prevalence of one of them or of 

 several in combination. Certain kinds of colloids, to which belong 

 the albuminoids, increase the viscosity of water considerably, and 

 almost directly proportional to their concentration. It is therefore 

 especially due to the colloids that some of the liquids of the organism 

 have a comparati^■elv high viscosity. 



As salts influence the pi'Operties of all colloids in a manner specific 

 for their ions (as we shall see later), they are also factors of the actual 

 internal friction of the organic colloidal systems, for instance, the vis- 

 cosity of glutin (Lewites) and gelatine (Schroeder) is 



Increased by Decreased by 



Na - CI, 80^, NC).;, acetate, oxalate Na - I 



K - CI, Br, SO, ' K - Br, I, NO.,, CNS 

 Li - CI, SO, 



NH, - CI, NO., SO,, PO, NH , - CI, NO.,, CNS 

 Mg - Cl.„ SO, 



Ba - CI, (KNO,, NH, NO,, in high 



Urea concentration) 



The eft'ect of the salts generally increases in propoi-tion as their 

 concentration increases. Hence the viscosity of an organic fluid is 

 the balanced result of the effects of the presence and concentration of 

 the colloids and the various kations, anions and non-electrt)lytes. 



The internal friction of the blood is nearly double that of plasma, 

 w^hich to the greatest extent has to be attributed to the presence of 

 the red blood corpuscles and then to the colloids of the plasma. 



