20 VITAL PHENOMENA GROWTH. [sect. 12. 



subsequently disappear as histologically separated structures, and 

 coalesce with the matrix connecting the cartilage-cells. Yet it 

 occasionally happens, particularly in the costal cartilages, and in 

 pathological articular cartilages, that the mother cells exist for a 

 long time and become filled with many generations of secondary 

 cells, which are either enveloped by the secondary or tertiary 

 mother-cells, or fill up the large capsule as a compact heap. 



With regard to the manner in which the nuclei multiply them- 

 selves in the different forms of cell-multiplication, this much is 

 certain, that the nucleoli always first divide into two and then 

 separate somewhat from each other. In certain cases, a simple 

 division of the nucleus may then follow, whilst in others, they 

 are formed endogenously in pairs in the enlarged mother-nucleus, 

 and become free by the resolution of the latter. In the yelk 

 segments of the ova of frogs, Remak found towards the termination 

 of the cleaving process, 2, 3 — 8 nuclei enveloped by one mother. 

 nucleus-membrane. 



§ 12. Vital Phenomena of fully developed Cells. — Growth. When 

 cells are once formed, a considerable number of functions appear 

 in them, which, like those of the entire organism, are divisible 

 into animal and vegetative. The latter relate to the form of the 

 whole cells and of their contents, as well as to their chemical 

 composition, and may be designated by the names of growth and 

 molecular changes. 



With regard to growth, it occurs, perhaps, in all cells, 

 although not everywhere in the same degree. It exerts its influ- 

 ence both upon the contents and upon the cell-membranes ; but 

 is, perhaps, chiefly dependent, in its peculiarities, upon the latter, 

 in which growth appears in a two-fold manner, inasmuch as they 

 either extend in superficial area or become thickened. The former 

 kind of growth is usually omnilateral, and hence cells may be- 

 come enlarged without change of form, as, for example ova 

 many nerve cells, etc., but is frequently unilateral as in all cells 

 which deviate in their form from the primitive spherical shape; 

 and, m this case, the cell-membranes deposit new material and 

 extend only at one or two or several points. Thickening of the 

 cell-membranes, with or without increase in superficial area, is to 

 be found in a greater or less degree in almost all cell-membranes, 

 all, perhaps, becoming somewhat firmer with age; yet it is 

 extremely difficult to decide in individual cases, whether such 

 thickening is owing to an increase of the membranes them- 



