516 
PHYSIOLOGY: J. LOEB 
discussion of the theory will be given in the complete paper. Those 
cases in which the possibility of diffusion through a membrane was 
diminished by the addition of too much salt or by a salt with bivalent 
cation have thus far been singled out for discussion under the heading 
of antagonistic salt action, but the proof furnished in this paper that the 
absence of electrolytes acts in a similar but more complete way shows 
that the case of antagonistic salt action is only a part of the more general 
problem of the role of electrolytes (or of the ionization of the protein 
molecules of the membrane) in the diffusion of salts through animal 
membranes. 
Summary and Conclusions. — Our experiments show that for the diffus- 
sion of certain electrolytes (potassium salts and acid) through animal 
membranes besides the osmotic pressure of the electrolyte a second 
effect is required which we call the ^salt effect' upon the membrane. 
This consists probably in an ionization of the protein molecules of the 
membrane. KCl and acid cannot diffuse through a membrane free 
from salts. The condition necessary for the diffusion of acid and KCl 
is produced when a trace of acid or a moderate amount of salt is added 
whereby the protein moleules of the membrane become ionized ('salt 
effect'). The addition of more salt (whereby the dissociation of the 
protein molecules of the membrane is diminished and probably other 
changes are brought about) annihilates this condition again. The 
latter fact is the special case of antagonistic salt action. The influence 
of the nature of the salt upon the limiting concentration for the 'salt 
effect' is stated in the paper. 
The nature of the forces by which the ionization of the protein mole- 
cules of the membrane may bring about the diffusion of acids and 
potassium salts (and possibly of electrolytes in general) will be discussed 
in the main paper. 
1 Loeb, J., these Proceedings, 1, 473 (1915); Loeb, J., and Cattell, McK., /. Biol. Chem., 
23, 41 (1915); Loeb, J., and Wasteneys, H., Biochem. Zs., 31, 450 (1911); 32, 155. 
2 Loeb, J., /. Biol. Chem., 23, 139 (1915); Science, 34, 653 (1911); Biochem. Zs., 37, 127 
(1912); Loeb, J., and Wasteneys, H., Biochem. Zs., 33, 489 (1911); 39, 167 (1912). 
