Chapter V 



THE STRUCTURE AND PROPERTIES OF SURFACES 



AND MEMBRANES 



In the previous chapters some of the fundamental phenomena causing 

 the destruction of the metabolic equilibrium of the normal cell after 

 x-radiation and gamma radiation absorption were examined. Many 

 substances will also decompose as the result of absorption of ultraviolet 

 rays. If these radiations can produce a modification in the surrounding 

 medium in which a cell is embedded, the resulting toxic products may 

 affect the life history of the cell. On the other hand, the energy may be 

 absorbed in such a way as to change directly the colloidal states of the 

 cytoplasm, causing a modification of the surface structure of the cell and 

 the accompanying alteration of the normal cellular permeability. 

 These modifications will permit the entrance of toxic chemical sub- 

 stances which are normally unable to enter the cell. 



A great deal of information exists regarding the passage of dissolved 

 substances into living cells and the accompanying changes in osmotic 

 pressure, but the interpretation of the data, particularly in regard to the 

 possible existence of plasmatic membranes, is rendered difficult by the 

 complexity of the system involved. In general, two points of view have 

 developed: (1) that the cytoplasmic surface is covered with a thin layer 

 of specially differentiated substances of a lipoid nature or with a mosaic of 

 alternate lipoid and protein material; (2) that no special membrane 

 exists on the surface of a cell, but that permeability phenomena are 

 governed by absorption of water by colloids and by the difference in 

 electrical potential which is developed as a result of the Concentration of 

 ions unable to cross the border of the cell. 



How far the membrane hypothesis is adaptable as an explanation of 

 cellular permeability and osmosis is left to the judgment of the reader 

 after he has acquainted himself with the phenomena contributing to the 

 changes in surface energy of liquids, existing either as free surfaces or 

 as surfaces of separation associated with partitions through which osmo- 

 sis can take place. 



Liquid Surfaces 



A liquid in a large-surfaced open container at rest and under the 

 influence of gravity develops a free horizontal surface. Below this free 



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