92 M. E. COLLETT 



greater for both organisms with fat-soluble than with non-fat- 

 soluble acids. And to some extent the reverse is true for Ca, 

 though the difference is not marked. 



Perhaps we can explain these results by assuming that the ac- 

 tion of each salt is double. Each has an influence upon phase 

 reversal: pure NaCl solution decreases the proportion of water- 

 insoluble lipoid and increases the water-soluble components 

 (such as Na-soaps in the external phase of the protoplasmic 

 emulsion, while CaClo has the opposite effect. In addition each 

 stabilizes the cell colloids against the swelling or coagulative action 

 of the H ion, CaCL better than NaCl. Sodium salts would 

 diminish the ability of the fat-soluble acids to penetrate the cell 

 by reducing the amount of Upoid or Ca-soap at the surface; 

 consequently Na should protect against them better than against 

 the non-fat-soluble acids which would be better able to penetrate 

 a Na-soap. Calcium would increase the water-immiscible lipoid 

 or soap and decrease the water-miscible soap at the surface, 

 and so would render penetration more difficult to water-soluble 

 acids and easier to fat-soluble acids, though this latter effect would 

 be at least partially balanced by its power to stabilize the proto- 

 plasm against the action of the H ion. The efficiency of a salt 

 would then depend upon the balance existing between its power 

 to protect the membrane against the entrance of the acid mole- 

 cule or anion, and its power to antagonize the H ion. Such a 

 theory would be in accord with the behavior of acids of the two 

 groups. Whether or not this explanation will hold in the form 

 given here, it appears probable, judging from observations on visi- 

 ble changes in the state of the protoplasm, that the action, what- 

 ever its precise nature may be, takes place largely at the surface. 

 Nierenstein*^ concludes from his work in vital staining that the 

 protoplasm of Paramecium, not only at the surface, but also within 



