STRUCTURAL BASIS OF THE HUMAN BODY. 17 



of irregular branched cavities, which communicate with each other, and 

 in wliich the branched cells lie: through these branching spaces nutritive 

 fluids can find their way into the very remotest parts of a non-vascular 

 tissue. 



- As a special variety of intercellular substance must be mentioned the 

 basement membrane (membrana propria) which is found at the base of 

 the epithelial cells in most mucous membranes, and especially as an in- 

 vesting tunic of gland follicles which determines their shape, and which 

 may persist as a hyaline saccule after the gland -cells have all been dis- 

 charged. 



(2) By anastomosis of their processes. 



This is the usual way in which stellate cells, e.g., of the cornea, are 

 united: the individuality of each cell is thus to a great extent lost by its 

 connection with its neighbors to form a reticulum: as an example of a net- 

 work so produced, we may cite the stroma of lymphatic glands. 



Sometimes the branched processes breaking up into a maze of minute 

 fibrils, adjoining cells are connected by an intermediate reticulum: this 

 is the case in the n^rve-cells of the spinal cord. 



Besides the Cell, which may be termed the primary tissue-element, 

 there are materials which may be termed secondary or derived tissue- 

 elements. Such are Intercellular substance, Fibres and Tubules. 



Intercellular substance is probably in all cases directly derived from 

 the cells themselves. In some cases (e.g. cartilage), by the use of re- 

 agents the cementing intercellular substance is, as it were, analyzed into 

 various masses, each arranged in concentric layers around a cell or group 

 of cells, from which it was probably derived (Fig. 6). 



Fibres. In the case of the crystalline lens, and of muscle both stri- 

 ated and non-striated, each fibre is simply a metamorphosed cell: in the 

 case of striped fibre the elongation being accompanied by a multiplication 

 of the nuclei. 



The various fibres and fibrillae of connective tissue result from a grad- 

 ual transformation of an originally homogeneous intercellular substance. 

 Fibres thus formed may undergo great chemical as well as physical trans- 

 formation: this is notably the case with yellow elastic tissue, in which 

 the sharply defined elastic fibres, possessing great power of resistance to 

 re-agents, contrast strikingly with the homogeneous matter from which 

 they are derived. 



Tubules which were originally supposed to consist of structureless 

 membrane, have now been proved to be composed of flat, thin cells, 

 cohering along their edges. (See Capillaries.) 



With these simple materials the various parts of the body are built up; 

 the more elementary tissues being, so to speak, first compounded of 

 VOL. I. 2. 



