210 



Comparative Animal Physiology 



TABLE 32. PARTIAL PRESSURE OF GASES IKI DRY AIR (760 mm. Hg) 



equivalent to sea water (20 gm. Cl/1.) and in blood, are presented in Table 33. 

 Although diffusion through a gas phase may be regarded as a simple func- 

 tion of the density and molecular size of the gas, diffusion through a liquid 



TABLE n. SOLUBILITY OF OXYGEN IN BIOLOGICAL FLUIDS 



ozzthe Bunsen Coefficient=the volume of gas (reduced to 0° C, 760 mm.) which at 

 the temperature indicated is dissolved in one volume of the solvent when the partial 

 pressure of the gas is 760 mm. (I.C.T.). 



must consider the concentration gradient, area, and time, and may be expressed 

 by the following derivation from Pick's law: 



dn RT dc 



dt " Nf dx 



dn representing the amount of substance diffusing across an area, a, in time 

 dt, with a concentration gradient_dc. R is the gas constant, T absolute tempera- 



dx 

 tare, N the Avogadro constant, and / the "frictional resistance" upon the 

 diffusing molecules. Simple diffusion processes can account for gas exchange 



TABLE 34. DIFFUSION CONSTANTS OF OXYGEN AT 20° C. 



Substance 



DifF. Const. 



Substance 



Diff. Const. 



Muscle""' 



Connective tissue"'" 

 Chitin-''"- 



0.14 



0.115 



0.013 



Water'^" 

 Gelatin"'' 



0.34 

 0.28 



through tissues for short distances, although exceptional cases of gas secretion 

 against a gradient have been demonstrated in a number of fish and in some 

 invertebrates.-""' Diffusion rates of oxygen in water and tissues are presented 



