THE PERMEABILITY OF CELLS 529 



KOH, let us say, would continue to diffuse in so long as neutralized 

 at a practically constant rate, it would require an enormous pro- 

 duction of acid on the part of the cell to take care of the KOH 

 entering. For this reason alone it seems safer to consider that 

 the inorganic alkalies do not enter (without affecting the surface 

 membrane) rather than that they are neutralized as they enter. 



There is, indeed, some evidence that an acid is secreted into the 

 vacuole of Elodea cells. If red stained leaves are placed in tv 

 NH4OH until color change occurs and then are immediately trans- 

 ferred to pure water, the cells are uninjured and the red color 

 returns. It is often a distinctly brighter red than before. I have 

 never noticed that Elodea cells placed in solutions of inorganic 

 alkalies became a brighter red before the color change finally 

 occurred. 



Again red stained leaves treated for one minute with chloro- 

 form water appear a slightly brighter red than the control. The 

 chloroform apparently induces the formation of an acid which 

 collects in the vacuole. Yet such leaves placed in to NH4OII are 

 decolorized slightly more rapidly than normal leaves and in tt 

 KOH, 30-40 times more rapidly. The experiment shows the 

 negligible effect of the acid in neutralizing entering alkali. 



The above considerations make the calculation of the strength 

 of any alkali entering a cell very difficult. We can state this 

 much, hpwever, we can give the concentration of alkali in terms 

 of the color change of the neutral red combination in each particu- 

 lar cell, and the relation of this color change to structural or 

 functional changes brought about by the presence of the alkali. 

 We must assume that when red becomes yellow the OH ion con- 

 centration of the various alkalies is equivalent. 



It must be borne in mind that the indicator in both Spirogyra 

 and Elodea is in the cell vacuole and that the alkali to reach it 

 must pass through the cell (plasma) membrane, the protoplasm, 

 and the vacuolar membrane. On the contrary, the indicator in 

 animal cells is in the protoplasm. 



