60 



GENERAL ANATOMY OF THE TISSUES. 



Fig. 10. 



Fig. 11. 



As to growth, it occurs perhaps in all cells, though not in all to the 

 same extent. It is clearly manifested in all those cells which are 

 formed directly round a nucleus, since in this case the membranes which 

 at first closely invest the nucleus, in time become more and more sepa- 

 rated, whilst the cells which arise around portions of contents or invest- 

 ing masses, and are from the first provided with contents, often 

 increase in size but very slightly. Growth is either in surface or in 

 thickness. The former appears very usually to be general, when cells 

 increase without altering their form, e. g. the ova, many nerve-cells, 

 &c. ; frequently however it is partial, as in all cells which depart from 

 the primitive globular form, in such a manner that the cell-membranes 

 only add new substance and extend at two or more points. Growth in 

 thickness also occurs, to a certain 

 extent, in all cells, since all cell- 

 membranes become somewhat 

 thicker with age : and it produces 

 in some localities a very consider- 

 able thickening of the membrane, 

 occasionally with evident lamina- 

 tion (as in the cartilage cells), and 

 even gives rise to certain structures (Fig. 11), which have the greatest 

 similarity to the sclerogenous cells of plants (bone-cells). 



The nuclei and nucleoli also take part, to a certain extent, in the 

 gro\vth of the cells. In the former, a general growth is easily demon- 

 strable in all growing cells ; in many, as in those of the smooth muscles, 

 of the epithelium of the vessels, of the formative cells of elastic tissue, 

 and others, there is also a partial growth, in consequence of which they 

 often assume the form of long slender rods. The nucleoli also not un- 

 frequently grow with their cells (nerve-cells, ova); but except when 

 dividing they never assume any but the globular form. 



Schwann has given an explanation of the growth, as well of the cell 

 as of the nucleus. He considers that the molecules of the cell-mem- 

 brane exert an attractive influence upon the fluid which surrounds them, 

 and deposits its newly-formed particles among themselves ; if the depo- 

 sition take place between molecules already present in the substance of 

 the membrane, the cell becomes distended ; if it take place only in the 

 direction of the radius of the cell, the membrane becomes thickened. 



FIG. 10. Cartilage cells of man. Two cells with thickened walls, from the cartilage of 

 the great cornu of the hyoidbone, containing a clear drop of fat beside their nucleus. Mag- 

 nified 350 diameters. 



FIG. 11. Six developing bone-cells from a rickety bone as yet sharply defined from the 

 interstitial substance: a, simple bone-cells; 6, a compound one, answering to a parent cell 

 with two secondary cells; c, similar ones with three cells. Magnified 350 diameters. 



* [This increased thickness of the cell-wall with age is well seen in all epithelial tissues 

 normal as well as pathological. 



