232 Permeability of Cells for Dyes and Alkalies [Dec. 



itself may enter. The changes undergone by Paramcrcium or 

 Elodea or the sea urchin tgg in NaOH must be the expression of 

 some profotind alteration of the cell surface involving one or all 

 of the properties mentioned above. Functional changes cannot, 

 therefore, be used as a criterion of permeability. 



The normal resistance of the surface of Elodea cells and sea 

 urchin eggs for NaOH can be diminished by the addition to the 

 NaOH of small concentrations of ether or Chloroform, too small to 

 produce any irreversible changes in the absence of the NaOH. 

 Ether and Chloroform induce the formation of an artificial fer- 

 tilization membrane about sea urchin eggs, but the amounts used 

 in testing their effects on the surface were too small to cause mem- 

 brane formation, although sufficiently great to inhibit the proto- 

 plasmic rotation characteristic of Elodea cells. Neutral salts 

 (NaCl, KCl and CaClg) also increase enormously the rate at which 

 the alkali enters Elodea. Nevertheless the protoplasmic rotation 

 may continue for hours in m/io NaCl. Thus, the modification 

 of the cell surface by NaCl is not correlated with a change in 

 functional activity (protoplasmic rotation), as is the modifica- 

 tion produced by ether or Chloroform. In some cases, namely in the 

 echinoderm tgg, a change in activity is associated with a normal 

 change in permeability. Just after sperm fertilization or artificial 

 fertilization the surface is much less resistant to NaOH than is that 

 of the unfertilized tgg. Evidence has recently been accumulated 

 by several observers which tends to show that the fertilized egg is 

 more permeable for various substances than the unfertilized, and 

 it is possible that an increase in permeability may be the factor 

 directly initiating development. 



The presence of traces of salts has a relatively great influence 

 in determining the properties of the cell surface. Thus, w/40 

 NaOH dissolved in pure redistilled water (quite harmless for 

 Paramoecia, a sufficient test of the purity of a water) enters 

 Elodea leaves in 25-30 minutes but the same n/40 NaOH dissolved 

 in tap water requires about 45 minutes to enter. The small pro- 

 portion of salts in tap water evidently confers on the cell mem- 

 brane quite different properties from those it would possess in the 

 absence of salts, i. e., in distilled water. The resistance of many 



