June 1, 1917] 



SCIENCE 



569 



one tissue of the body to another. We must 

 assume that the fat in the gastric epithelial 

 cells is present in normal animals in ultra- 

 microscopic or very nearly ultramicroscopic 

 aggregates, and that the circumstances attend- 

 ant upon anaphylactic shock have merely in- 

 duced coalescence of the preexisting fat gran- 

 ules into aggregates sufficiently large to be 

 identifiable as fat. 



The existence of a considerable proportion 

 of ultramicroscopic fat-granules in living cells 

 which is thus established provides a material 

 basis for the assumption of a diphasic struc- 

 ture in which the one phase is permeable and 

 the other impermeable to substances soluble in 

 water but insoluble or relatively insoluble in 

 fats. 



The most usual spatial arrangement of the 

 various structures or constituents of a cell is 

 that of radial symmetry. The primitive ar- 

 rangement of strictly radial symmetry so fre- 

 quently displayed in spherical cells becomes 

 modified or distorted in those cells, such as 

 the majority of epithelial cells, which through 

 mutual compression, or for other reasons, have 

 assumed a columnar, stratified or flattened 

 outline. In such cases the radial arrangement 

 of structures may be confined to the sides or 

 margins of the cell or differ in character 

 in the protoplasm underlying the various 

 facets of the cell. 



A radial arrangement of the ultramicro- 

 scopic fat granules of the cell would obviously 

 lead to the formation upon the surface and in 

 the subjacent protoplasm of minute funnel- 

 shaped pores, of which the interstitial open- 

 ings would be permeable to substances soluble 

 in water, while the walls, being composed of 

 fat granules, would be impermeable or with 

 difiiculty permeable by such substances. The 

 interstitial openings at the margin distal from 

 the center from which the fat granules radiate 

 would be relatively large, while at points lying 

 nearer to the center of radiation, that is, in 

 general, deeper within the cell, even if the 

 radiating lines of globules should not be con- 

 tinued sufficiently far in that direction to 

 actually intersect one another, the diameter 

 of the pores would be very considerably con- 

 tracted. Substances soluble in water would 



penetrate such a cell readily, since a rela- 

 tively large proportion of the cell-surface 

 would consist of the water phase, but they 

 would leave the interior of the cell with diffi- 

 culty, since a relatively large proportion of the 

 area which they would have to traverse to at- 

 tain an outlet would consist of the lipoid 

 phase. If the modifications of radial sym- 

 metry which are so characteristic of epithelial 

 cells should result in the confinement of this 

 structure to one surface or facet of the cell it 

 is obviously possible that one-sided permeabil- 

 ity of a tissue composed of such cells might be 

 the consequence. 



It should be borne in mind that the exist- 

 ence of funnel-shaped pores in the surface of 

 a cell or membrane would only give rise to 

 one-sided permeability provided the diameter 

 of the pore at the constricted end were com- 

 parable with the mean free path of the pene- 

 trating molecules. Were the least diameter 

 of the pores less than the mean free path of a 

 given molecule, then the membrane would be 

 a strictly semipermeable one for this type of 

 molecule; were it, on the contrary, very large 

 in comparison with the mean free path of the 

 molecule concerned, then the membrane would 

 be freely permeable by the molecule in either 

 direction. Thus it is readily conceivable that 

 membranes of this type might exhibit one- 

 sided permeability for certain substances dis- 

 solved in water, absolute permeability for 

 others, and semipermeability for yet other 

 molecules. 



Any reagent or condition affecting the state 

 of aggregation of the fat globviles would nec- 

 essarily affect the diameter of the pores. In 

 general those conditions involving the forma- 

 tion of large aggregates would increase the 

 permeability of tissue by enlarging the diam- 

 eter of the radiating droplets and therefore 

 that of the interstitial spaces. Moreover, since 

 the droplets are suspended in a protoplasmic 

 gel, we may infer that in all probability their 

 radial dispersal would be modifiable by altera- 

 tions of the state of aggregation of the proteins 

 of the cell. The relationship of lipoid solu- 

 bility and of lipoid solvents and of substances 

 which have a marked effect upon surface ten- 

 sion to the permeability of cells thus find an 



