INTRINSIC ACTIVITY OF SECRETING CELLS 261 



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 contained 

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

 in the plasma, but furnish no means for obtaining substances 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 been undertaken 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 anesthetics 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 

 or not in the lipoid membrane, and hence can obtain ingress to 

 the cell. The author does not state in the case of the anaesthetics 

 whether the action is to be ascribed to the physical action upon 

 the lipoids themselves, or whether it is due to a passage through 

 the lipoids to the cell protoplasm. 



Friedenthal has evolved a similar theory for the absorption 

 of fats in the intestine, which he ascribes to the high solubility 

 of the fats in the protoplasm of the absorbing cells. The theory 

 is also extended to other substances taken up in solution for ab- 

 sorption or secretion, so that these processes are placed in dependence 

 upon the peculiar and selective properties of the cell as a solvent. 



The two theories of the lipoid membrane acting as a selective 

 solvent and of the cell protoplasm playing a similar role may be 

 taken together, as the same arguments apply to both views. 



Neither of these theories furnishes any basis of explanation of 

 how energy is expended in concentrating any secreted or absorbed 

 substance. For the fact that a substance, such as the lipoids 

 or cell protoplasm, is a good solvent for a given constituent does 

 not give any power to the solvent to pass that substance through 

 the cell in more concentrated solution, or indeed to alter the con- 

 centration of the dissolved substance anywhere save in the solvent 

 Further, increased concentration in the solvent has no 



