18 



consisting of bodies called lipoids, 1 related to the fats and 

 lecithins, are supposed to be easily permeable for some substances 

 such as urea, ammonia, carbonic-ions, and the anaesthetics ; but 

 difficultly or almost impermeable for other substances such as the 

 usual inorganic ions of the plasma, viz., potassium, sodium, phos- 

 phates and chlorides. As a result of this difficult permeability it 

 is supposed that the potassium is retained in the cell, and the 

 sodium in the plasma, while anaesthetic, ammonia, and urea, for 

 example, rapidly pass through. 2 



There are, however, fatal objections to this membrane view, 

 viz. first, that while it makes some attempt at an explanation of 

 the maintenance of the status quo, it fails entirely to explain how 

 that condition was originally arrived at ; secondly, it inextricably 

 confuses factors which are of value in the velocity with which 

 equilibrium is arrived at with the final conditions of equilibrium ; 

 and thirdly, it fails to explain the phenomena of cell interchange 

 and the rapid physiological effects upon the cells of variations in 

 the concentration of the ions in the external medium. 



If the cell is almost impermeable to potassium ions, for example, 

 it is difficult to see how it has become fully charged with them, 

 and to many times the amount that these are present in the nutrient 

 fluid outside. 



Again, however poor the permeability, if there is no union 

 between constituents within or without and the ion in question, it 

 is obvious that when equilibrium has finally been attained, the 

 concentrations at the two sides must be equal. Variations in 

 permeability can only alter the time required to reach equilibrium, 

 and not the final conditions of accumulation on the two sides 

 corresponding to the equilibrium. 



Further, ana?sthesia cannot, as has been suggested by the 

 upholders of the membrane theory, arise from greater solubility 

 of the anaesthetic in the membrane, because that would only delay 



1 The text merely refers to linoids regarded as semi-permeable membranes. 

 Using lipoid as a generic term to include the class of the lecithides and other forms 

 of compound fats, there is no doubt that these play an important role in the life 

 of the cell by means of their power of entering into combination or absorption with 

 organic poisons and toxins. But this is entirely different from a membrane action, 

 being a formation rather of easily dissociable unions of the kind shown in tin- text 

 to exist between bioplasm and organic bodies. 



2 The questions of cell permeability, and the' arguments for the membrane 

 view, may be found in detail in Hamburger's Oxmntiwhi'r Jirtn-l- mnl Lnu'n /</</>. 

 For the reasons givon in the text they have not been stated at length. 



