144 PROTOPLASMIC ACTION AND NERVOUS ACTION 



benzol, which is almost insoluble in water, while ether 

 is readily soluble (to the extent of about 12 volumes 

 per cent) and penetrates the partition. Experiments 

 illustrating the same principle may be performed with 

 gases; thus if a tube, containing air, closed below with 

 a water-soaked membrane and connected above with a 

 manometer, is placed in a vessel of ammonia or hydro- 

 chloric acid gas, the pressure rapidly rises in the tube 

 because of the penetration of the water-soluble gas 

 through the water-layer. Ramsay's well-known experi- 

 ment with a tube filled with nitrogen and separated 

 from a hydrogen atmosphere by a palladium partition 

 (at 350° to 400°) illustrates the same general phenomenon; 

 hydrogen but not nitrogen penetrates the partition, 

 hence the pressure rises within the tube.^ 



In all of these cases the permeability of the partition 

 depends on its consisting (in part) of some material 

 which acts as a solvent to the penetrating substance. 

 Nernst called attention to the possibility that similar 

 conditions might exist in living cells; i.e., that the 

 solubility of substances in constituents of the proto- 

 plasmic membranes might be the condition of their 

 selective absorption by cells; and this form of explanation 

 was later adopted by Overton who reached the conclu- 

 sion, as a result of his studies on permeability already 

 described, that the protoplasmic surface layer consisted 

 chiefly of compounds with solvent properties similar to 

 those of typical organic solvents. 



Later, chiefly because of experiments indicating a 

 parallelism between the penetration of various acid and 

 basic dyes into living cells and the solubility of the same 



^ Ramsay, Z. physik. Chem., V (1894), 518. 



