22 PROTOPLASMIC ACTION AND NERVOUS ACTION 



condition for the isolation of chemical and physiological 

 processes in adjacent regions of the organism is the 

 presence of the semi-permeable intercellular partitions. 



There is also evidence that the internal protoplasm of 

 the single cell is frequently pervaded by a system of films 

 or closed partitions giving a chambered type of structure ; 

 and the possibility of intracellular chemical differentia- 

 tion ('' chemical organization") has been referred to 

 this condition.^ Such a chambered structure corresponds 

 essentially to that of an emulsion-like or alveolar system. 

 Apparently any physico-chemical system which is 

 built up largely of water and substances in aqueous 

 solution must be a partitioned system if it is to maintain 

 within a small space a high degree of chemical differ- 

 entiation together with a corresponding diversity of 

 chemical activity. 



In general, each living cell can be shown to possess 

 a surface layer (plasma membrane) with properties differ- 

 ent from those of the internal protoplasm. At the boun- 

 dary between this surface layer and the adjoining medium 

 the general phenomena characteristic of phase-boundaries 

 are exhibited. A highly characteristic feature of the 

 living cell is that its surface is sharply defined against 

 the medium, like the surface of an oil drop, very much 

 as if the surface layer consisted of water-insoluble 

 material. This water-immiscible property of living 

 protoplasm and the semi-permeability of its boundary 

 layer are closely associated properties; together they 

 constitute one of the most noteworthy physical peculiari- 

 ties of living protoplasm. Especially significant is the 



^ Hofmeister, Die chemische Organisation der Zelle, Braunschweig 

 (1901). 



