

V 



FIG. 28. Reticular tissue from lymph- 

 node. X 300. 



CONNECTIVE TISSUE. 23 



stance. Where the latter is best developed, it is composed of delicate fibres 

 which resemble those of fibrous connective tissue. The reticular fibres prob- 

 ably differ somewhat from the white fibres of connective tissue in chemical 

 composition, containing a variety of gelatin known as reticulin. Reticular 

 tissue occurs principally as the supporting 

 framework of lymphoid tissue, hence is well 

 seen in suitably prepared sections of the 

 lymph-nodes and of the spleen. It is also 

 found in the mucous membrane of the intes- 

 tinal tract, while the reticulum of bone-marrow 

 and the interstitial tissue of certain organs, 

 as the kidneys and liver, contain it. 



Fibrous Tissue. Under this head are 

 included the more usual forms of connective 

 tissue which have representation in, practi- 

 cally, all parts of the body. They exhibit 

 a wide range of variation in their physical 

 properties which depend upon differences 

 in the intercellular substance, due to modi- 

 fications in the arrangement and propor- 

 tions of its constituents. Before considering the several varieties of fibrous 

 connective tissue, loose and dense, the histological components common 

 to all these tissues claim attention. These components are the cells and 

 Oa& fibres. 



Connective Tissue Cells. Although the more active constituent of the 

 connective tissue, it is only in the youngest and immature stages that 

 the cells are conspicuous; later, after the tissue has acquired its definite 

 characteristics, the intercellular substance has usually become so predomi- 

 nant, that the cells are reduced to inconspicuous elements, notwithstanding 



their important role as nutritive and reproductive 



centres. The irregularly branched or stellate types 

 of the parent mesenchymal cells are retained 

 ordinarily only during the earlier periods of growth, 

 the connective tissue cells decreasing in size and 

 prominence as the intercellular substance increases 

 in amount and differentiates into definite bundles 

 of fibres. In the adult tissues, with few exceptions, 

 the cells appear as small fusiform or flattened 

 elements, in which the deeply staining oval nucleus, 

 surrounded by a small amount of cytoplasm, serves 

 as the chief means of detection. Being thicker 

 than the cell-body, the nucleus projects beyond 

 the general level of the cell and, viewed in profile, 

 appears as a colored linear elevation embedded 

 in a plate of faintly tinged cytoplasm. Since 

 the cells depend for their nutrition on the tissue- 

 juices which occupy the clefts or lymph-spaces 

 between the bundles of fibres, the relation of the connective tissue cells 

 to these bundles is constant and characteristic for, wherever definite 

 bundles are present, the cells are applied to the surface of the fasciculi. 

 Where the latter are closely packed, the juice-channels form a system of 

 intercommunicating spaces or canals, seen in dense tissue after staining 

 with argentic nitrate, when they appear as light, irregularly stellate figures 



FIG. 29. Young connective 

 tissue cells from subcutaneous 

 tissue of cat embryo. X 590. 



