On analogous effects exerted by antagonistic calcium and citrate ions in physical and biological systems

From the preceding paper it appears that antagonistic kations and anions exert their effect upon the equilibrium of aqueous oil systems by causing variations in the relative solubility of a concentration film of fatty acid salts in oil and water. The resemblance between the effects observed in purely physical systems of this type and in biological systems suggests the possibility that protoplasm may consist essentially of an aqueous lipoid system in which a film of lipoid material functions as the continuous phase. If this is the case, an excess of either positive or negative ions should exert a disturbing effect upon the physical equilibrium of the protoplasm corresponding with that observed above, and a critical point at which kations and anions exactly counterbalance one another should be found in biological systems corresponding with that observed in purely physical systems, the precipitation of lipoids and fatty acid salts, for example.

To test this question calcium was selected as a suitable kation, and citrate as a suitable anion on account of the facility with which the proportions in which they counterbalance one another in the process of blood coagulation may be estimated (see subsequent communication). A m/5 CaCl₂ and a chemically equivalent solution of sodium citrate were prepared and admixed in varying proportions ranging from 0 per cent. of Ca and 100 per cent. of citrate to 100 per cent. of Ca and 0 per cent. of citrate. On mixing these solutions with aqueous sodium oleate suspension, the following results were obtained.

Precipitation was complete from IOO per cent. to 40 per cent. of calcium, gradually diminishing from this point until virtually no precipitation was visible between 35 per cent. and 30 per cent. of calcium, once more rising to an almost complete precipitation between 25 per cent. and 5 per cent. and subsequently diminishing until the solution containing no calcium and 100 per cent. citrate gave no precipitation.