156 INTRINSIC ACTIVITY OF SECRETING CELLS 



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 afterwards 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 

 absorption 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 furnish 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 

 itself. Further, increased concentration in the solvent has no 

 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 0, 



