CHAPTER VI 



PROTOPLASMIC STRVCTVRE— Continued: PERMEA- 

 BILITY AND OTHER PROPERTIES OF 

 PROTOPLASMIC MEMBRANES 



We have seen that the stabiHty of emulsion systems 

 and many of their essential properties are determined by 

 the presence of thin interfacial films. In the formation 

 of these films, and in the determination of their special 

 properties, electrical and other factors enter, of a kind 

 characteristic of boundary surfaces in general. In 

 general, it may be said that heterogeneous mixtures 

 containing substances that influence the surface-tension 

 or the electrical polarization at the phase-boundaries 

 tend to reach a state of equilibrium in which they have 

 what may be called a ''structure"; i.e., a more or less 

 orderly and definite distribution of the components. 

 The gathering of surface-active compounds at the 

 phase-boundaries, in conformity with the principle 

 of Gibbs and J. J. Thomson, is a chief factor determining 

 the character of this distribution; and the latter second- 

 arily determines the character of the chemical changes 

 occurring in the system. Living protoplasm is an 

 example of a heterogeneous system in which the control 

 of chemical change by structural conditions has reached 

 perhaps its highest development. 



Not only are the structural elements of protoplasm 

 (alveoli, nuclei, colloidal particles, fibrils) bounded by 

 surfaces at which adsorption and chemical change 

 occur, but the whole mass of protoplasm, the Hving 



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