CHANGES OF CELLS IN THE 



Fig. XIV. 



growing cells meet one another, they generally become angular or poly- 

 hedral ; and this change may be combined with elongation into the pris- 

 matic or flattening into the tabular form, as exemplified in the columnar 

 and scaly varieties of epithelium. A more remarkable change of figure 

 occurs in those instances where a cell sends out branches at various 

 points of its circumference, as happens with 

 certain varieties of pigment-cells (fig. xiv.), 

 connective tissue corpuscles, and nerve-cells. 

 Of course, when the changes of figure are accom- 

 panied by an absolute increase in size, there must 

 be assumption of new matter by the cell. The 

 nucleus seems to be less subject to alteration in 

 s-ize and shape. It may grow somewhat larger 

 as the cell increases, especially at first ; thus it 

 enlarges and flattens in epithelium-cells. In 

 the cells of non-striated muscle it becomes oblong 

 or rod-shaped. Sometimes it disappears, as in 

 the flattened cells of the cuticle. 



2. Whilst the above -described changes of figure 

 are going on, the cell- wall may acquire increased 

 density and strength ; and in a flattened cell, 

 when much extended, the opposite sides may co- 

 here so as to convert it into a scale. The thicken- 

 ing of the cell-membrane may take place by 

 deposition of new matter on its inner surface, as 

 in vegetable cells, or on the outside, as is pro- 

 bably the case in the partial thickening of the 

 cell-wall in certain forms of intestinal epithelium ; 

 but there are cases in which it is difficult to 



determine in what way the change is effected. The substance of a cell thus 

 condensed may have changed more or less in chemical nature, as in the 

 cuticle, where the cells, while deep-seated and recently formed, are soluble 

 in acetic acid, but as they rise to the surface lose this property and acquire 

 a horny character. 



3. Changes may take place in the cell- contents. Granular matter in 

 cells may be dissolved and consumed, as is well seen in the formation of 

 blood- corpuscles from granular cells in the oviparous vertebrata. On the 

 other hand, new matters may appear, as fat and pigment within the adipose 

 and pigmentous cells, and the peculiar constituents of certain secretions in 

 the cells of secreting organs, in which last case the cells may burst and dis- 

 charge their contents. Lastly, the process may take on more of a plastic 

 and organising character, as in the generation of young cells, already 

 described, and the formation of the spontaneously moving bodies named 

 spermatozoa, which are produced from the nuclei of cells. 



These plastic changes are equally unexplained with the other alterations of form 

 and structure which accompany the production and metamorphoses of cells. As 

 regards the changes in the quantity and chemical nature of the contained matter, it 

 may be remarked, that the introduction of new matter into a cell is so far a phe- 

 nomenon of imbibition, and, as such, must be to a certain extent dependent on the 

 endosmotic effect produced by the substance already within the cell, and on the 

 comparative facility with which the matter to be introduced is imbibed and transmitted 

 by the permeable cell-wall. Some substances, moreover, being more readily imbibed 

 than others, the quality as well as the quantity of the imbibed material will be so far 



Fig. XIV. RAMIFIED AND 

 FUSIFORM CELLS, FROM THE 

 TISSUE OF THE CHOROID 

 COAT OF THE EYE ; MAG- 

 NIFIED 350 DIAMETERS 

 (after Kolliker). 



a, cells with pigment ; 

 b, colourless fusiform cells. 



