THE CELL 281 



In brief our conclusions so far are: Every cell at its surface 

 possesses a membrane which is dependent upon the composition of 

 the interior of the cell. This membrane may be visible and may 

 have been formed through the gelatinization of the cell protoplasm at 

 the periphery. It may, on the other hand, be so thin as to be in- 

 visible, being formed by the concentration and spreading out of such 

 albuminous and fatty colloids as diminish the surface tension of the 

 cell content at the interface. The cell membranes, developing as a result 

 of the gelatinization of cell protoplasm, are at first, in youth, expansile 

 and elastic; with increasing age these membrane colloids, depending 

 upon their environment and upon chemical influences, or as a result 

 of mere colloid aging phenomena, become poor in water and lose their 

 elasticity. 



[In his " Growth and Form," Cambridge, 1917, D'ARCY W. THOMP- 

 SON invokes the aid of colloid phenomena in discussing the dynamics 

 of cell life. Tr.l 



