PHYSIOLOGY: /. LOEB 
515 
cation, like Na, they will recover. In experiments on the diffusion 
of KCl into the egg these salts acted somewhat differently, Mg and 
especially Ca inhibiting the diffusion. 
TABLE III 
Intluence of Cation upon the Recovery 
PERCENTAGE OF EMBRYOS POISONED BY KCl RECOVERED AFTER 
TWENTY-FOUR HOURS IN 
00 
VO 
00 
0 
0\ 
00 
10 
10 
0 
0 
0 
0 
S 
s 
e" 
\ 
s 
a' 
\ 
s 
"e 
s 
W 
LiCl 
30 
45 
80 
60 
80 
60 
30 
5 
0 
10 
5 
NaCl 
90 
100 
100 
100 
100 
90 
40 
25 
15 
10 
0 
RbCl 
0 
0 
0 
5 
5 
0 
1 
0 
2 
0 
0 
CsCl 
5 
5 
0 
0 
5 
5 
0 
0 
0 
0 
MgCl2 
100 
85 
95 
75 
55 
25 
25 
25 
15 
10 
5 
CaCl2 
100 
100 
75 
45 
20 
20 
SrClz 
30 
15 
30 
15 
20 
0 
5 
25 
0 
0 
10 
BaCl2 
5 
0 
5 
10 
15 
25 
10 
20 
35 
10 
20 
0 
NH4CI 
38 
72 
89 
83 
77 
41 
16 
15 
15 
11 
N(C2H5)4C1 
100 
78 
60 
23 
20 
14 
5 
14 
12 
10 
3. If we wish to formulate a theory of the general ^salt effect' upon 
the membrane required to make the diffusion of potassium salts possible, 
we must remember that the conditions for the diffusion of acid into the 
egg resemble those described for KCl.^ We know that acids form salts 
with proteins, which dissociate rather completely into protein ion and 
the anion of the acid used; while ordinarily the protein molecule (being 
usually a very weak base and acid) does not dissociate electrolytically 
to any extent. We can understand the phenomena described in this 
paper if we assume that the ionization of the proteins of the membrane 
is the prerequisite for the diffusion of KCl as well as of acid through the 
membrane. When this ionization of proteins of the membrane is to 
be brought about by neutral salts, as in the case of the diffusion of KCl, 
a much higher concentration of the salts is required than when the 
ionization is caused by acid or base, and the limiting concentration 
varies with the constitution of the salts. This ionizing effect need not 
be produced entirely by KCl but, for the ^salt effect,' the KCl can be 
partly replaced by other neutral salts. When more than a moderate 
amount of salt is added the ionization of the proteins of the membrane 
is diminished instead of increased, and the diffusion of KCl may again 
become as impossible as if a non-electrolyte had been added. A fuller 
