752 



SCIENCE 



[N. S. Vol. XLIII. No. 1117 



ceivable that the former approximates to a dis- 

 persion of proteins, fats, lipoids, and other 

 colloids in water, while the latter approximates 

 to the reverse type of system in which water is 

 more or less dispersed in an outer or continu- 

 ous phase of fats, lipoids, and possibly proteins. 

 Arguments in support of the view that proto- 

 plasm when &st formed is a system rela- 

 tively freely permeable to water because water 

 is the outer or continuous phase are, first, 

 the active Brownian movement exhibited by 

 protoplasm when inspected by means of the 

 ultra microscope; and, second, the freedom 

 with which water-soluble substances, artifi- 

 cially introduced through the protoplasmic 

 film, permeate the protoplasmic material. 

 Arguments in support of the view that the 

 protoplasmic film is relatively impermeable to 

 water, because water is more or less dispersed 

 in an external or continuous phase, consisting 

 at least in part of fats and lipoids, are, first, 

 the resistance offered by the protoplasmic film 

 to the passag'c of salts, sugars, and other water- 

 soluble substances; second, the resistance to 

 the passage of an electric current; third, the 

 phenomenon of osmotic pressure; fourth, the 

 variations in the proportions of given elec- 

 trolytes within and without the cell ; and, fifth, 

 the freedom with which anesthetics and other 

 fat solvents penetrate the protoplasmic system. 

 Since the variations in permeability of proto- 

 plasm under the influence of salts of Ca and 

 ISTa may well be attributable to a reversal of 

 phase relations analogous to that observed in 

 the case of emulsions, sols and jellies, the next 

 question to determine is whether given elec- 

 trolytes exert antagonistic effects on physical 

 systems in the same ratios as on living ceUs. 

 Before describing the experiments, it is neces- 

 sary to refer briefly to the explanation offered 

 by Bancroft for the apparently antagonistic 

 action of soaps of K'a and Ca in emulsion sys- 

 tems. Pure oil and water when shaken to- 

 gether do not give a permanent emulsion. 

 Soap or some other so-called emulsifying agent 

 must be employed. The emulsifying agent 

 exerts its effect by concentration at the inter- 

 face between oil and water, forming a film 

 which prevents the subsequent coalescence of 



the dispersed particles. Bancroft concluded 

 that soaps of N^a, which are freely dispersed in 

 water but not in oil, form a film which is 

 wetted more readily by water than by oil, with 

 consequently a lower surface tension on the 

 water than on the oil side, and, since the area 

 of the inside face of a film surrounding a 

 sphere is smaller than that of the outside face, 

 the film will tend to curve in such a manner 

 as to enclose globules of oil in water, thus re- 

 ducing the area of the side of higher surface 

 tension to a minimum as compared with that 

 of lower surface tension. Conversely, a film 

 composed of Ca soap, which is freely dispersed 

 in oil but not in water, is wetted more readily 

 by the oil than by the water, the surface ten- 

 sion is lower on the oil than on the water side, 

 and the film tends to curve in such a manner 

 as to enclose the globules of water in an outer 

 or continuous oil phase. 



While studying reversible emulsion systems, 

 the writer observed that when those electro- 

 lytes, like CaCL,, that promote the formation 

 of an emulsion of water in oil are present in 

 such proportion as to balance those, like iNaOH 

 or l^aCl, that promote the formation of an 

 emulsion of oil in water, a critical point is 

 recognizable at which neither type of emulsion 

 predominates, and the oil and water separate 

 rapidly under the influence of gravity into 

 two layers. This observation affords a strong 

 support of Bancroft's conclusion. Since the 

 electrolytes in question are exerting an exactly 

 compensatory effect on the film it has no tend- 

 ency to curve in either direction, and, since it 

 remains straight, neither phase is capable of 

 surrounding the other. The mixture shaken 

 together really contains two continuous phases 

 analogous to the fiber and air in a sponge, and, 

 since oil and water are both fluids, they sepa- 

 rate readily under the influence of gravity. 



Salts of divalent and trivalent cations, and, 

 under certain circumstances, small amounts of 

 acids appear to function in the same way as 

 salts of Ca, promoting the formation of emul- 

 sions of water in oil. Alkalies, salts of mono- 

 valent cations, and of di- and trivalent anions, 

 appear to function similarly to Na OH,. pro- 

 moting the formation of emulsions of oil in 



