144 E. E. FEEE 



nal, discontinuous phase will be near together or far apart ac- 

 cording to the relative volume of the two phases; that is, accord- 

 ingly to the size and number of the globules relative to the value 

 of the medium in which they are suspended. But this ratio 

 of the volumes of the two phases depends upon the distribution 

 of the water between them. If water passes out of the globules 

 into the medium there will be an increased volume of the medium 

 (external phase) and a decreased volume of the globules (internal 

 phase) . If water passes in the reverse direction the total volume 

 of the globules will increase and that of the medium will de- 

 crease. If the number of globules remains the same this may be 

 expressed in terms of size. When water passes from medium to 

 globules the globules swell; when it passes in the reverse direction, 

 they shrink. Of course there are corresponding changes in the 

 distances between globules or, what is the same thing, in the 

 average thickness of the layers of medium between them. It is 

 possible to imagine the globules so large that they are packed 

 closely together to the point of mutual deformation, the medium 

 being reduced to a system of thin films between the swollen glob- 

 ules. This condition appears to be realized in many gels. On 

 the other hand, it is possible to imagine the globules so small 

 that they are far apart and touch but seldom, as in most emulsoid 

 sols. 



The bearing of these considerations on permeability will be 

 apparent if these changes are imagined as taking place in the 

 surface layet of protoplasm. It may be remarked, however, 

 that the reasoning holds equally well for any protoplasm in any 

 part of the cell and does not depend on the assumption of a differ- 

 entiated surface layer or Plasmahaut. Considering the sur- 

 face layer of the cell, whether differentiated or not and regard- 

 ing it as a two-phase system of the kind described, it is obvious 

 that when the globules of the internal phase are small there will 

 be wide spaces of medium between them. At such times sub- 

 stances soluble in the medium will enter the cell readily. On the 

 other hand when the globules are large the spaces between them 

 will be small, perhaps reduced to mere films, and substances 

 soluble in the medium cannot enter, or will enter only with 



