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PROCEEDINGS OF THE AMERICAN ACADEMY. 



tion tlian simply the uubalauced partial pressures of the salts comes into 

 play. It is well kuown that in experiments on osmosis a membrane 

 may during the course of the experiment alter its constitution in conse- 

 quence of having, for example, a greater affinity for the solvent than for 

 the solute. Thus a copper ferrocyanide membrane (Schiifer, '98, Vol. I, 

 p. 275) absorbs water. Some such process as this I conceive to take 

 place with Stentor in distilled water. Absorption of water by the cell- 

 wall or the protoplasmic meshwork might very probably result in a 

 permeability for the contained salts much greater in degree than its 

 normal permeability. Furthermore we do not know what important 

 changes in metabolic processes the presence of more water than normal 

 might entail. The processes of molecular condensation, perhaps indi- 

 cated by greater or less relative dryness of protoplasm, give indications 

 of being of fundamental importance in the anabolism and katabolism of 

 living organic matter. Whatever the process may be, the presence of an 

 extremely high concentration of water is its efficient condition, and it is 

 this same condition that is absent in the hyperisotonic application of 

 milk sugar and of salts also. If, then, the protoplasmic membrane 

 swelled, and so increased its permeability to an abnormal degree in dis- 

 tilled water, such swelling would be absent in hyperisotonic media of 

 milk sugar and physiological salts. The permeability of the cell could 

 be less than normal, especially toward the outward movement of its 

 physiologically necessary salts. This condition by no means necessitates 

 the preclusion of the entrance of a single salt existing externally under 

 high pressure. Some membranes, for example the shell membrane of 

 the hen's e^g and the skin of the frog (Schafer, '98, Vol. I, p. 280), are 

 known to be permeable to a particular substance in one direction only. 

 The outward movement of salts with unbalanced partial pressures into 

 distilled water is due to the alteration of tlie permeability of the membrane 

 by contact with water free from salts. Milk sugar, on the contrary, does 

 not alter the normal permeability, which presumably does not permit the 

 escape of salts physiologically necessary to the life of the cell. It seems 

 quite probable that abnormal alteration of the important membrane that 

 mediates nearly all interchange between the surrounding liquid and the 

 cell contents, is a frequent, perhaps constant, factor in the action of salts 

 and other agents upon free-living cells. The physiological condition of 

 the membrane may embrace such a variety of possibilities that physico- 

 chemical analysis cannot proceed far without the determination of this 

 factor. This is a difficult undertaking, that must be made in each par- 

 ticular case. 



