50 DEVELOPMENT OF THE TISSUES FROM CELLS. [CHAP. I. 



pointed processes, which unite arid form the ramifications of the 

 vessels. 



In these examples, the nucleus of the cell appears to take no 

 part in the formation of the tissue. What becomes of it ? does it 

 become absorbed, or does it waste away, its office having ceased? 

 There is abundant evidence to shew that the nuclei are still per- 

 sistent in the fully formed tissues, for they have been seen in all 

 those enumerated in the last paragraph. They are generally altered 

 in form, being flattened and elongated. Henle believes that, while 

 they retain their peculiar characters, they are prolonged at either 

 pole into peculiar fibres, distinct, in anatomical and chemical cha- 

 racters, from the proper fibres of the tissue : he designates the 

 latter Zellenfasern, cell-fibres ; and the former Kernfasern, nucleus- 

 fibres. For instance, the two elements of areolar tissue, which 

 will be described at a future page, are derived, according to him, 

 the white fibrous element, from the cell; the yellow, from the 

 nucleus. The formation of the homogeneous simple membrane 

 which forms the basement of the skin and mucous membrane, may 

 be ascribed to the flattening and fusion of the cell- walls into one 

 another. The free surface of these membranes, wherever they may 

 be found, whether as integuments to the body, or folded into glands, 

 is the seat of a continual development of new cells, which may 

 have primarily sprung from the nuclei of the formative cells of the 

 basement membrane. 



In other tissues the walls of the cells become thickened by a 

 deposition around and between them, with which they become 

 united and incorporated, and thus an intercellular substance is 

 formed. This substance becomes the seat of a further deposition, 

 or new arrangement of particles, which, as far as we know at pre- 

 sent, is not preceded by the development of cells. In cartilage, 

 which in its simplest state is only an aggregate of cells, this sub- 

 stance assumes a fibrous form. In most textures, it is not im- 

 probable that the nuclei are persistent ; in cartilage, they remain 

 in the cell-cavities, and possibly contribute to the growth and 

 nutrition of the cartilage ; in bone they form the lacunae from 

 which minute canals are prolonged into neighbouring ones, or into 

 the vascular channels ; and, in teeth, they are probably converted 

 into the dental tubuli. 



From the preceding brief and necessarily imperfect sketch, it 

 seems evident, that, in the various metamorphoses of the foetal into 

 the perfect tissues, both the elements of the cells take a part. In 

 no instance does there appear to be an actual conversion of either 



