CRYSTALLOID IN LIVING CELLS 317 



of bodies called lipoids, 1 related to the fats and lecithins, are sup- 

 posed 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 inor- 

 ganic ions of the plasma viz., potassium, sodium, phosphates, 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 corre- 

 sponding to the equilibrium. 



Further, anaesthesia cannot, as has been suggested by the up- 



1 The text merely refers to lipoids regarded as semipermeable 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 cells 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 the 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 " Osmotischer Druck und lonen- 

 lehre." For the reasons given in the text they have not been stated at length. 



