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Mr. J. Gray. 



containing balanced cations. In the latter type of solution the hydroxyl 

 ions outside the cell cannot penetrate the cell, nor can the anions outside 

 the cell exert any influence upon the uptake of water by the cell. Such a 

 condition of affairs is obviously due to the semi-permeable nature of the 

 normal cell membrane. The inference to be drawn is ; of course, that when 

 placed in a solution of a pure sodium salt the observed effects are the direct 

 outcome of the loss of semi-permeability by the cell membrane. Direct 

 proof of this statement is provided by a determination of the electrical 

 conductivity of normal tissues placed in pure sodium salts. Osterhout (8) 

 showed that the electrical resistance of Laminaria tissue placed in sodium 

 chloride solution fell steadily, until it was one-third of its original value ; 

 Gray (4) showed that sodium citrate caused a marked fall in the resistance 

 of Echinoderm eggs, and quite recently Shearer (11) has shown the similar 

 effects of sodium chloride on bacteria. 



(c) The Nature of the Cell Membrane. 



Lillie(7) showed that the toxic effect of pure sodium salts is prevented 

 by the presence of the alkaline earth metals. This has been confirmed and 

 the statement can be somewhat enlarged. In the first place, either 

 magnesium or calcium can prevent the destructive action of a pure sodium 

 chloride solution upon the cell-membrane ; or, as is perhaps the more correct 

 mode of expression, the presence of magnesium or calcium is necessary 

 for the semi-permeable properties of the cell membrane. Since both calcium 

 and magnesium occur in sea-water, it is of importance to determine, if 

 possible, which of these two metals maintains the normal stability of the 

 cell surface. 



In the following experiment the concentration of each salt was the 

 concentration in which it normally occurs in sea-water.* 



NaCl Ph 7 "0 Complete disintegration after 3 hours. 



NaCl + CaCL Ph 7'0 No disintegration after 24 hours. Some cilia 



destroyed, and some filaments separated from 



their neighboui's. 



NaCl + MgCL Ph 7 "0 Tissue quite healthy, but cilia motionless after 



24 hours. 



It is clear that the amount of magnesium in normal sea-water is alone 

 capable of maintaining the cell-surface : at the same time the amoun t of 

 calcium is also sufficient to produce a very well-marked stabilising influence. 

 In the solution which contains only calcium and sodium in their normal 



* The composition of the sea- water used was : — NaCl, 28'3 grs. per litre ; KC1, 0"76 grs. 

 per litre ; MgCl 2 , 5 "01 grs. per litre ; CaCl 2 , 1"22 grs. per litre. 



