458 Permeability 



penetrated through the plasma membrane, but this may have 

 taken place wholly or in part before the nitrates were added to the 

 sea water. 



The mechanism by which nitrates and potassium are stored 

 within the cell so as to remain at a higher concentration than in 

 the surrounding sea water deserves further study. 



It is of interest that the cell wall acts as an osmotic membrane 

 but possesses no selective permeability. Dead cells are often 

 turgid even though the protoplasm has shrunken away from the 

 cell wall. These cells when put into a hypertonic salt solution 

 almost immediately become flaccid, and when replaced in sea 

 water or in fresh water they again become turgid. However, 

 if dead cells are placed in water containing nitrates, nitrate can 

 be demonstrated within them shortly afterwards. If living cells 

 are killed and then replaced in sea water, sulfate can soon be 

 shown to be present inside. This shows that salts can pass more 

 or less freely through the cell wall and yet it offers sufficient 

 obstruction to enable it to act as an osmotic membrane. 



The writer takes pleasure in expressing his thanks to Professor 

 E. L. Mark for the use of the facilities of the Bermuda Biological 

 Station, where this investigation was made, to Professor W. J. 

 V. Osterhout for his interest in the problem and many helpful 

 suggestions, and to an unknown friend who assisted in bearing 

 the expenses of the Bermuda trip. 



