Penetration of Marine Tissues by Alkali. 137 



PART II. PERMEABILITY AND FUNCTIONAL CHANGE. 



THEORETICAL. 



Two quite opposite points of view have been taken by physiologists in 

 regard to the relative importance of the permeability of cells. Some regard 

 the cell-surface as of no consequence in regulating cell processes, being freely 

 permeable at all times to crystalloidal substances in the medium or in the 

 cell. Others see in the surface an important regulator of chemical reactions 

 in the cell and a barrier of a high degree of impermeability, retaining cell 

 constituents as a test-tube retains the substances reacting within its walls. 

 Theoretically, no more simple method of regulating the velocity of chemical 

 reactions could be found than by means of a membrane whose permeability 

 to the reaction product might vary. Actually, there is a large mass of 

 evidence indicating that the cell-surface is a highly impermeable membrane 

 for substances normally occurring in or used by cells. The evidence has 

 been advanced in numerous papers by Lillie® and Hoeber^ and need not be 

 discussed here. 



Crucial evidence has only recently been put forward that the cell-surface 

 (particularly its permeability) plays an important part in cell activities — 

 that it may vary at different periods of activity and in the presence of 

 definite substances. 



The evidence may be classified under three heads: 



1. Measurements of permeability changes induced by narcotics, anaes- 



thetics, and salts or other substances which affect cell activities. 



2. Measurements of permeability during different states of functional 



activity. 



3. Determinations of the rate of penetration of a substance and rate of 



change in functional activity induced by the substance. 



PERMEABILITY CHANGE THROUGH CHEMICALS. 



Of particular interest here is the experiment of Osterhaut,^ in which it 

 is shown most clearly by the plasmolytic method that the plasma membrane 

 possesses greatest impermeability to salts in a balanced medium or in the 

 medium which most nearly approaches that of the normal. Pure NaCl or 

 pure CaCl2 both enter Spirogyra cells or marine algae slowly, the latter more 

 slowly than the former; but if the two are mixed in the proportions of a 

 balanced solution, they mutually retard each other's entrance. The NaCl, 

 alone in solution, must increase the permeability of the plasma membrane 

 to such an extent that its entrance is greatly facilitated. 



Osterhaut' has recently confirmed his results, mentioned above, by the 

 electrical conductivity method of measuring permeability. Disks cut from 

 the kelp, Laminaria, were placed face to face so as to form a cylinder several 

 centimeters long, and its conductivity was measured. In NaCl the con- 

 ductivity of the c^dinder was found to increase regularly (as compared with 



•Lillie.R. S. Amer. Jour. Physiol., vol. 24, p. 14. 1909; vol. 28, p. 197. 1911. Also Biol. Bull., 27, 192. 



1909. 

 ' Hoeber, R. Physikalische Chemie der Zelle und Gewebe., 3d Aufl. 1911. 

 ' Osterhaut, W. J. V. Science, n. s., vol. 34, p. 187. 1911. 

 • Osterhaut. W. J. V. Science, n. s., vol. zs, P- 112. 1912. 



