TITF. rOXXECTIVE TISSUES 91 



round on cross section, the larger flattened or hexagonal (Figs. 45 

 and 46). Their elasticity is easily demonstrated in teased specimens 

 by curUng of the broken ends of the fibres (Fig. 32). On boiUng 

 they yield elastin. Although, when subjected to the usual technic, 

 elastic fibres appear homogeneous, they are probably composed of a 

 thin sheath or membrane, enclosing the more granular elastin. The 

 latter stains intensely with magenta, the sheath remaining unstained. 



In addition to the white fibres and elastic fibres above described, 

 so-called ''reticular" fibres are frequently present in fibrillated 

 connective tissue. (See p. 99.) 



{b) Basement or ground substance constitutes the matrix in which 

 the connective-tissue cells and fibres lie. It also occurs in extremely 

 minute amounts between the Individual fibrill.T of the white fibres, 

 where it acts as a cement substance (Fig. 31). Difiiculty in seeing 

 this ground substance is due to its transparency. It may be demon- 

 strated by staining with silver nitrate. (See technic 9, p. loi.) 



Much variation exists in regard to the proportions of the different 

 elements. This gives rise to variations in the physical characteristics 

 of the tissue. When fibres predominate over cells and ground sub- 

 stance, the tissue is dense and hard and is known as dense fibrous tissue. 

 The terms fine connective tissue and coarse connective tissue desig- 

 nate the character of the fibres. When many cells are present, the 

 tissue is softer and is known as cellular connective tissue. 



According to the arrangement of the white fibres, fibrous connec- 

 tive tissue is subdivided into areolar or loose connective tissue and 

 formed connective tissue. 



Areolar or Loose Connective Tissue 



In this the fibres are irregular, running in all directions and in- 

 terlacing, leaving between them meshes or areolce (Fig. 32). 



Subcutaneous connective tissue is a typical example of areolar 

 tissue. Both white and elastic fibres are present, although the former 

 predominate. Areolar tissue varies greatly as regards the relative 

 number of cells and fibres and the closeness with which the different 

 elements are packed. It thus varies greatly in density. 



Fat Tissue, — Adipose tissue or fat tissue is a form of areolar 

 tissue in which some of the cells have become changed into fat cells. 

 Fat tissue is peculiar among the connective tissues in that the cells and 

 not the intercellular substance make up the bulk and determine the 



