LIPOID-ALTERANT SUBSTANCES 207 



Changes of permeability, of viscosity, and of resist- 

 ance to the action of cytolytic or other injurious condi- 

 tions are the most evident physical effects produced by 

 lipoid-alterant compounds in living protoplasm. During 

 narcosis there appears very generally to be a decrease of 

 permeabihty, an increase in the resistance to structural 

 breakdown or cytolysis, and an increase of protoplasmic 

 viscosity. From the general nature of these changes it 

 would seem that the structural substratum of the Uving 

 matter assumes temporarily a denser or physically more 

 stable condition. In any event it is clear that the 

 modification is in such a direction as to interfere with 

 stimulation, a process, which (as we shall see later) 

 involves structural changes in the irritable system. 

 Hence what may be described as a stabilization, decrease 

 of susceptibiHty to structural change, is indicated as in 

 all probabiHty the essential physical condition underlying 

 narcosis; but any such general term gives little indication 

 of the detailed nature of the physical modification 

 produced in the living protoplasm. The manner in 

 which narcosis modifies stimulation-processes will be 

 considered in more detail later; in the present section 

 we shall merely describe briefly those changes in the 

 physical state of protoplasm which appear to have some 

 bearing on the question of the nature of the conditions 

 determining narcosis. 



The changes observed in the larva of Arenicola are 

 simple and instructive; normal larvae transferred from 

 sea water to pure isotonic NaCl solution undergo stimula- 

 tion and marked increase of permeabihty as shown by 

 loss of pigment; on the other hand, larvae which are 

 first placed in a solution of a magnesium salt, or in sea 



