Dae Proteins 
the surest method of producing ionized proteins was to treat 
proteins with either acid or base. It was generally found that 
when a protein with little tendency to electrolytic dissociation is 
treated with acid of the right concentration a protein salt is 
formed which undergoes a strong electrolytic dissociation, while 
the addition of a neutral salt diminishes this degree of dissociation, 
as was to be expected. Loeb and Wasteneys,’ and later the writer 
alone,’ were able to show that the toxic effect of acid can be di- 
minished or suppressed by the addition of neutral salts. This 
was the first direct support of the idea that antagonistic salt ac- 
tion was due to a transformation of lonized protein into electrically 
neutral protein. 
The second case where it seemed possible to attribute antago- 
nistic salt action to a transformation of ionized into non-ionized 
protein consisted in the observation that the diffusion of a low 
concentration of KCl into the egg of Fundulus is impossible or 
extremely slow when this salt is alone in solution, but is rendered 
possible through the addition of a small amount of a second salt, 
e.g. NaCl (‘‘salt effect’), and that the diffusion of KCl is ren- 
dered impossible again when more of the second salt is added. 
The analogy with the solubility of globulin suggested that the 
addition of a small quantity of the second salt caused an ioniza- 
tion of some protein in the membrane of the egg which was sup- 
pressed again by the addition of more salt; and the writer ex- 
pressed this idea in a preliminary notice.’ But this suggestion 
faces the uncomfortable fact already referred to that according © 
to Hardy globulins form non-ionized molecules with neutral 
salts.? 
The writer, however, has found a method which suggests 
strongly that the antagonism between NaCl and CaCl, is due— 
at least in the case to be discussed—to the fact that an ioniza- 
tion of protein is caused by NaCl and that this ionization or its 
effect upon the swelling is suppressed by a comparatively small 
quantity of CaCl. 
5 Loeb, J., and Wasteneys, H., Biochem. Z., 1911, xxxili, 489; 1912, xxxix, 
167. ; 
6 Loeb, J. Biol. Chem., 1915, xxiii, 189; 1917, xxxii, 147. 
7 Loeb, Proc. Nat. Acad. Sc., 1916, ii, 511. 
