GENERAL MORPHOLOGY OF TLIE CELL 



19 



We may therefore still accept as valid the definition given more than 

 thirty years ago by Leydig and Max Schultze, that a cell is a mass (§5"^ 

 of protoplas7n containing a nucleus} to which we may add Schultze's 

 statement that botJi nuclens and protoplasm arise through the division 

 of tJie corresponding elements of a preexisting cell. Nothing could be 

 less appropriate than to call such a body a "cell " ; yet the word has 

 become so firmly established that every effort to replace it by a 

 better has failed, and it probably must be accepted as part of the 

 established nomenclature of science.^ 



A. General Morphology of the Cell 



The cell is a rounded mass of protoplasm which in its simplest 

 form is approximately spherical. The form is, however, seldom 

 realized save in isolated cells such as the unicellular plants and ani- 

 mals or the egg-cells of the higher forms. In vastly the greater 

 number of cases the typical spherical form is modified by unequal 

 growth and differentiation, by active movements of the cell-substance, 

 or by the mechanical pressure of surrounding structures, but true 

 angular forms are rarely if ever assumed save by cells surrounded by 

 hard walls. The protoplasm which forms its active basis is a viscid, 

 translucent substance, sometimes apparently homogeneous, more fre- 

 quently finely granular, and as a rule giving the appearance of a 

 meshwork, which is often described as a spongelike or netlike " reticu- 

 lum."^ Besides the active substance or protoplasm proper the cell 

 almost invariably contains various lifeless bodies suspended in the 

 meshes of the network ; examples of these are food-granules, pig- 

 ment-bodies, drops of oil or water, and excretory matters. These 

 bodies play a relatively passive part in the activities of the cell, 

 being either reserve food-matters destined to be absorbed and built 

 up into the living substance, or by-products formed from the proto- 

 plasm as waste-matters or in order to play some role subsidiary to 

 the actions of the protoplasm itself. The passive inclusions in the 

 protoplasm may be collectively designated as metaplasm (Hanstein) 

 ox paraplasm {Ysx\^^tx\ in contradistinction to the 2LCi\ve protoplas7n. 



^ Leydig, Lehrhuch der Histologic, p. 9, 1857; Schultze, ^r^/;. Anat.u. Phys.,^. 11, 1861. 



2 Sachs has proposed the convenient word energid {Flora, '92, p. 57) to designate the 

 essential living part of the cell, i.e. the nucleus with that portion of the active cytoplasm 

 that falls within its sphere of inlluence, the two forming an organic unit both in a morpho- 

 logical and in a physiological sense. It is to be regretted that this convenient and appro- 

 priate term has not come into general use. (See also Flora, '95, p. 405, and cf. Kupfifer 

 ('96), Meyer ('96), and KoUikcr ("97).) 



^ Such meshworks are sometimes plainly visible in the living protoplasm (p. 44). It is 

 always more or less an open (piestion how far the appearances seen in fixed (coagulated) 

 material corresponti with the conditions existing in life. See pp. 42-46. 



