540 Proteins 
paring the effects of washing with MgCl. and MgSO, and of CaCl, 
and CaSO,. When we perfuse powdered gelatin first with m/8 
NaCl and then with CaCl, solutions of a higher degree of dilu- 
tion we must expect a lower limit of concentration where the 
swelling begins, since CaCly by replacing the NaCl in combina- 
tion with gelatin transforms the ionizable gelatin into a less ion- 
izable or otherwise modified complex. The concentration of 
CaCl, must therefore become comparatively low before swelling 
becomes possible. If the additional swelling, 7.e. the ionization 
of the gelatin, depends on the cation alone or predominantly, 
CaSO, and MgSO, should have the same critical concentration for 
the commencement of the swelling, which is the case, as Table 
IV shows. The critical concentration for all the salts is M/512. 
TABLE IV. 
Additional swelling of powdered gelatin perfused twice with 25 ec. m/8 
NaCl and then three times with 25 cc. of the following solutions. 
e/2/8)/e]/2]8& | s)/2/8)8 |e] 9 
3 an ae 2 3 sf s >|. epee Pe | 
MgCl ie... Oe - 0 0 0 020 4 13. (26). 142 49 | 53 | 52 
MgoO ay. ee letayre (8) —l; 0 1 5/22 5138 48 | 55 | 638 
CaCls: aii: ares 0 0 0 0 1L.5i 8) 1245, 139 48 | 51 | 47 
CasO7 ek tee —3.5|—2.5|+8.5)18.51387.5| 48 | 47 | 55 
SrGle sce ee 0 0 0 0} O 1 8 |18 |36 AS) Dj 2abos 
Bah yerehee | 0 0 0 0} O 1 10 {21 /40 45 | 51 | 50 
All these facts support the idea that neutral salts form com- 
pounds with gelatin which dissociate into a positive metal ion 
(that of the salt used) and into a negatively charged protein ion 
which may or may not contain the anion of the salt. This idea 
was tested by experiments on the migration, in an electric field, 
of gelatin treated with m/8 NaCl and then freed from the salt 
by washing. Such gelatin migrates to the anode as our theory 
demands. ti 
ITI. 
The idea that only the cation enters into the ionization of 
gelatin might be interpreted to mean that a reaction of the fol- 
lowing kind occurs between gelatin and NaCl: 
