262 INTRINSIC ACTIVITY OF SECRETING CELLS 



effect whatever upon rate of passage of the substance through 

 the solvent or through the cell, and will indeed delay passage 

 through the cell until the lipoid or cell protoplasm has become 

 saturated with the dissolved substance, and after that will behave 

 in an inert manner, without any effect either upon uptake of dis- 

 solved substance, rate of passage of dissolved substance through 

 the cell, or output of dissolved substance at the other side. 



In the statement of the two theories there is a complete con- 

 fusion of solubility and permeability, which are quite distinct 

 processes. , 



The matter may perhaps be most easily made clear by means 

 of a diagram. 



Suppose we have a sphere of fluid C, surrounded by a continuous 

 layer of a different fluid B, and immersed in a vessel containing a 



quantity of fluid A, and that A 

 contains a substance x in solution. 

 Further, that the substance is also 

 soluble in the fluids B and C, and 

 that the coefficient of distribution 

 of the substance x is such between 

 the three fluids, that the concentra- 

 tions of /3x in B and of yx in C 

 correspond to the concentration ax 

 p IG ^ in A, so that there is equilibrium 



when the ratio of concentrations is 



ax :/3x :yx in the three fluids A, B, and C. Now if at the commencement 

 there is none of x in B or C but x is present in A, diffusion into B will 

 take place, and as soon as the concentration of x in B commences to rise 

 there will be diffusion from B into C. Also, the higher the value of 

 the ratio /3:a, the more rapid, other things being equal, will be the rate 

 of entry of x into B ; but if /3 be increased so as to increase the ratio /3 : a, 

 the ratio y:/2 which determines the rate of output into C will be 

 correspondingly diminished, and hence the rate of passage from A to C is 

 entirely independent of the solubility in B, and depends only upon the 

 rate of transmission or diffusion through B. 1 Also the final condition 

 of equilibrium is independent of the solubility in B, for A and C are 



1 The matter may also be put thus the rate of solution from A into B 



r\ 



is given by fc x , that of solution from B into C by & 2 ^, therefore that from 

 A into C is given by k^ - . k. 2 L or K ^. 



