1. It is shown that NaCl acts like CaCl2 or LaCl3 in preventing the diffusion of strong acids through the membrane of the egg of Fundulus with this difference only that a M/8 solution of NaCl acts like a M/1,000 solution of CaCl2 and like a M/30,000 solution of LaCl3.
2. It is shown that these salts inhibit the diffusion of non-dissociated weak acid through the membrane of the Fundulus egg but slightly if at all.
3. Both NaCl and CaCl2 accelerate the diffusion of dissociated strong alkali through the egg membrane of Fundulus and CaCl2 is more efficient in this respect than NaCl.
4. It is shown that in moderate concentrations NaCl accelerates the rate of diffusion of KCl through the membrane of the egg of Fundulus while CaCl2 does not.