366 RALPH S. LILLIE. 



mined. It would appear that the peculiar properties of the 

 membrane depend upon its being a living structure, the seat of a 

 specific metabolism. That the characteristic semi-permeability 

 depends on this latter peculiarity is seen in the fact that the 

 death-process, however induced, is always associated with a 

 marked increase in the general permeability and electrical con- 

 ductivity of cells. In other words, the normal semi-permeable 

 condition involving, as it must, a certain constancy in the 

 composition and physical state of the surface-film is maintained 

 only so long as the cell remains alive. This fact shows that semi- 

 permeability, and the electrical polarization which is associated 

 with this, are not simply static properties of the plasma-mem- 

 brane, but are functions of a specific metabolic activity includ- 

 ing probably oxidations in most cases which maintains constant 

 the physico-chemical characteristics of the surface-layer of proto- 

 plasm. In the irritable element this metabolism appears to be 

 altered in a definite manner by changes in the electrical polariza- 

 tion of the membrane; and along with these chemical alterations 

 go alterations of permeability and, secondarily, of electrical 

 polarization. These latter involve the production of local elec- 

 trical circuits which traverse and hence stimulate the adjoining 

 inactive portions of the irritable element; in this manner the 

 state of excitation spreads, and the whole element is stimulated. 1 

 But this is the case provided only that the membrane retains 

 its normal sensitivity to changes of electrical polarization; if it 

 has previously been rendered resistant by an anaesthetic, no such 

 effect follows; the element as a whole then shows itself irre- 

 sponsive to stimulation. 



1 For a fuller discussion cf. my papers on the conditions of conduction in irritable 

 tissues, already cited. 



