INTRINSIC ACTIVITY OF SECRETING CELLS 155 



since it cannot increase, as we have seen, the concentration above 

 the value in the lymph, and if it had the value of the lymph (or 

 water) in permeability, the concentrations would be practically 

 the same. It is when the permeability changes in the opposite 

 direction, and the degree of permeability of the secreting or absorb- 

 ing cell becomes progressively less and less than that of a layer 

 of lymph or water of equal thickness, that the only and indeed 

 an important effect of cell permeability becomes obvious, in slowing, 

 never in hastening, the rate of secretion of constituents. For as 

 the permeability of our imaginary secreting or absorbing lamina 

 to any constituent becomes less and less, its resistance to the 

 passage of that constituent becomes greater and greater, and the 

 concentration of the constituent in the secretion or absorbed fluid 

 less and less, until in the limit none may pass through at all. 



It is in such a resisting action that the value of differences in 

 permeability comes in, by causing the retention of substances 

 in the lymph, and not in a high degree of permeability causing 

 increased rate of passage, and increased concentration of sub- 

 stances in secretion. Examples are the retention of the plasma 

 proteids in the glomerular secretion or filtration, and the pre- 

 vention of ingress of poisonous substances in many cases to the 

 tissue cells. But the greater concentration of substances and ions in 

 the secretions cannot be explained by the application of the principle 

 of altered permeability. Diffusion and permeability can accord- 

 ingly explain the passage of such substances as are already con- 

 tained in the plasma up to the concentrations at which they are 

 contained in the plasma, but furnish no means for obtaining sub- 

 stances not present in the plasma, or for concentrating crystalloids 

 or ions in solution to osmotic pressure higher than in the plasma. 

 The latter effects, which are universal in processes of secretion and 

 absorption, can only be obtained from expenditure of energy by 

 the cell. 



An attempt has recently been made by Overton and Meyer 

 and by Friedenthal to explain the secretion and absorption of 

 substances by the cell on the basis of varying solvent powers of 

 the cell or certain of its constituents for such substances. 



Thus Overton would explain the effects of anaesthetics as arising 

 from the high solubility of the anaesthetic in the lipoids or lecithin 

 of the cell, and also the absorption or non-absorption of other 

 substances by the cell as dependent upon whether they dissolve 



