April 7, 1916] 



SCIENCE 



505 



electrolytes or non-electrolytes which, when 

 brought into contact with the cell surface, 

 would reduce the degree of dispersion of the 

 surface colloids. This process is not, how- 

 ever, a simple reciprocal of liquefaction. A 

 slight increase in the aggregation of the sur- 

 face colloids would involve a rise in the vis- 

 cosity of the cell surface and, if an equilibrium 

 were established, the speed of diffusion of 

 ions and molecules across the cell surface 

 would thus be reduced. As we noted above, 

 the speed of diffusion of any substance across 

 the cell surface is one index of the degree of 

 permeability of the cell for that substance. 

 Hence we may say that with an increase of 

 viscosity at the surface, the permeability of 

 the cell would be decreased. If now the concen- 

 tration of the agent that is responsible for the 

 increased aggregation at the cell surface were 

 still further increased, there would be an addi- 

 tional increase in the viscosity of the surface. 

 But, as we have already stated, the viscosity of 

 colloids is sharply limited by the state of 

 aggregation of the disperse phase. When the 

 precipitating disperse phase begins to sepa- 

 rate out from the dispersion medium, the vis- 

 cosity suddenly decreases. Similarly, when at 

 the surface of the cell the disperse phase be- 

 gins to separate from the dispersion medium, 

 the fluidity of the cell surface must rise 

 abruptly. The sharp increase in fluidity would 

 obviously involve a sudden removal of the bar- 

 rier to diffusion for ions and molecules and 

 they would pass the cell surface more rapidly.' 

 From the above considerations it seems, 

 therefore, that the permeability of a cell may 

 be increased either (1) by bringing into con- 

 tact with the surface a solution of some lique- 

 fying agent like a thiocyanate, i. e., some 

 agent that increases the solubility (degree of 

 dispersion) of the surface colloids and the 

 fluidity of the surface, or (2) by bringing into 

 contact with the surface a solution containing 

 an excess of some deliquefying or precipitating 

 agent like CaCl^ which, by increasing the state 

 of aggregation of the surface colloids eventu- 

 ally separates disperse phases from solvent, 



9 Ostwald, Wolfg., '11, Grundriss d. KoXloid- 

 chemie, 2 Aufl., p. 307. 



the fluidity of the cell surface approaching 

 that of the pure dispersion medium. 



The normal influences at the cell boundary 

 must have a considerable aggregating effect 

 upon the surface colloids since we do not 

 normally find the cell pigments or other con- 

 stituents diffusing outwards. Osterhout,'-° 

 furthermore, has shown conclusively that cer- 

 tain electrolytes increase the electrical resist- 

 ance of a cylinder of Laminaria discs. This 

 is to be considered an expression of decreased 

 permeability. These electrolytes (MgCl^, 

 CaCl„ HCl, La.CN'O^),) all have, in certain 

 concentrations, a distinct coagulative or de- 

 hydrating effect upon a variety of colloids.''- 

 The effect of CaCL is of particular interest 

 since at first it increases the resistance. After 

 a time, however, the resistance again decreases, 

 finally falling below the initial value. This is 

 precisely what we should expect if the effect 

 of the CaCl^ were upon the viscosity of the 

 surface colloids. The theoretical correlation 

 between increased dispersion and increased 

 permeability, as well as that between increased 

 aggregation and initial decreased permeability, 

 is thus actually substantiated by experiment. 



Permeability studies upon living cells have 

 brought out one very striking and at first sight 

 anomalous, fact, viz., for many substances which 

 are not concerned with the normal metabolic 

 processes of the cell, the cell surface is read- 

 ily permeable, whereas for sugars, salts, amino 

 acids, etc., which must constitute a large pro- 

 portion of its nutritive material, it is nearly 

 or quite impermeable. The latter substances 

 normally occur, however, vrithin the cell, which 

 forces us to assume that at some previous 

 period the surface must have permitted their 

 passage to the cell interior. This passage to 

 the interior of the cell could have been accom- 

 plished only under conditions of increased 

 permeability. 'Now the cell content is ob- 

 viously not to be regarded as permanent and 

 fixed and we must account for a mechanism 

 of metabolic interchange. Such a mechanism 



10 Osterhout, W. J. V., '15, Science, 41, 255 for 

 a summary of regults. 



11 Mines, G., '10, Jour, of Physiol, 40, 327; 

 '11, ibid., 42, 309; Hober, B., u. Spaeth, B. A., 

 '14, Pfliigers Arch., 159, 433. 



