PERMEABILITY AND THE PROTOPLASMIC MEMBRANE 291 



bility theory of narcosis may, therefore, be justly formulated, 

 but the theory fails when applied to other forms of anesthesia, 

 e.g., when caused by salts. Magnesium sulphate is an excel- 

 lent narcotic; chloral hydrate is a still more powerful one, and 

 it is several times more soluble in water than in oil. While 

 the parallelism between lipoid solubility (disturbance of perme- 

 ability) and narcotic action is not a perfect one, yet high lipoid 

 solubility is typically associated with pronounced narcotic 

 action. 



Permeability of the Protoplast as a Whole. — Permeability 

 studies are usually based on the assumption that there is a plasma 

 membrane and that it is responsible for permeability phenomena. 

 As the membrane is of protoplasm, there is no reason why the 

 permeability properties assigned to the membrane should not 

 be applicable to the protoplasmic mass as a whole. Indeed, 

 some workers ascribe all permeability phenomena to the proto- 

 plasm as a whole and not to the surface layers alone. Protoplasm 

 is a jelly; the taking up of water by it must therefore involve 

 imbibition, and this is but a form of permeability. Freundlich 

 emphasizes the importance of swelling in natural processes. 

 Hofler states that the permeability of protoplasm for water is 

 not unlimited but, on the contrary, is rather slight; i.e., there is 

 control (see also page 278). De Haan says that changes in the 

 water permeability of protoplasm are the expressions of changes 

 in the swelling of protoplasm. In the same way that the water 

 permeability of the cell is determined by the entire protoplasmic 

 mass, just so may certain permeability phenomena be properties 

 of the protoplasm as a whole instead of properties of the surface 

 layer alone. 



Conclusion. — All of the foregoing hypotheses of membrane 

 mechanics have an element of truth in them. Pore size, chemical 

 constitution, electric charge, surface tension, adsorption, imbibi- 

 tion, the orientation of linear molecules, and the Donnan equilib- 

 rium, operating collectively rather than singly, probably 

 determine the selective permeability of the living protoplasmic 

 membrane. 



