THE BIOLOGY OF THE CELL SURFACE 



(both nuclear and cytoplasmic ground-substance) by differ- 

 ences in physical properties, in structure and in behavior; as 

 part of the cytoplasm, as differentiated ground-substance, 

 it is definite!}' a living part of the cell. The inner region of 

 the cytoplasmic ground-substance plus its cytoplasmic 

 inclusions — granules and the like — is defined as the endo- 

 plasm. 



It is not to be supposed that ecto-endoplasmic differ- 

 entiation in animal cells was unknown before Haeckel's 

 time. Although not named as such, those regions were 

 known to the older students of the cell.^ Almost any 

 original paper and text-book of theirs points out differences 

 between the inner and the outer region of the extranuclear 

 cell-contents. Thus, Henle in reports of his researches and 

 Koelliker in his text-book on human histology gave clear 

 descriptions of what subsequently were known as ectoplasm 

 and endoplasm. Kidney, liver and intestinal cells were 

 both described and figured to show these regions. The 

 cells of the skin were favourite objects for such descriptions. 



If one observes a section of the kidney taken from man or 

 other vertebrate one notes that certain cells are striated and 

 possessed of radial projections. Thus, these cells reveal an 

 ectoplasmic differentiation. 



The ectoplasmic area is less clearly marked off in the 

 human liver cell. The manifold functions of the liver — the 

 breaking down of red blood corpuscles, the formation of 

 urea, the storage of sugar as glycogen, the mobilization of 

 fat — are reflected in the many pictures of itself that the 

 small polyhedral liver-cell can exhibit. It also appears 

 differently in conditions of hunger and after rich nourish- 

 ment. Nevertheless, in all its different appearances, the 

 liver-cell shows a differentiation between inner and outer 

 regions of the cytoplasm, as Koellicker observed. 



^ For example: Leydig, /S^y; Kiihne, /864. 



7(^ 



