CONNECTIVE TISSUE. 25 



are often designated " wandering cells" as distinguished from " fixed cells," 

 as the connective tissue elements proper are then termed. The lymphocytes 

 exhibit the usual characteristics of their class (see Blood, page 97) and 

 appear as small irregular cells in which the spherical deeply stained nucleus 

 is surrounded by a narrow zone of cytoplasm. Occasionally larger elements, 

 the plasma-cells, are seen in the vicinity of developing blood-vessels'. 

 They are probably derived from the lymphocytes, but differ from these in 

 their much larger size, greater amount of readily staining cytoplasm, and 

 markedly eccentric nucleus. Their cytoplasm stains deeply with basic dyes 

 and contains fine but indistinct granules. Two other forms of free 

 cells, the mast-cells and the eosinophiles, are conspicuous by reason of the 

 coarse granules with which their cytoplasm is laden. The mast-cells are 

 irregularly round or oval in shape and possess an oval nucleus (Fig. 33). 

 The coarse granules are deeply 

 colored by basic dyes but prone 

 to change. The eosinophiles are C^w ^~~ 



. \0B < . %U 





;ue of 



FIG. 32. Pigmented connective tissue cells from FIG. 33. Mast -cells from submucous tiss 



choroid. X 400. mouth; v, v, blood-vessels. X 825. 



distinguished by large granules which, while staining with acid dyes, possess 

 an especial affinity for eosin, after the action of which they appear copper-red. 

 Under the name, clasmatocytes, have been described irregular branched cells 

 with long processes and scattered coarse granules. These elements are, 

 perhaps modifications of the basophilic lymphocytes, which they resemble 

 in granulation and staining reactions. 



Connective Tissue Fibres. The intercellular substance of fibrous con- 

 nective tissue includes two varieties of fibrillar constituents, the white 

 fibres and the elastic fibres. Both of these probably arise by the differenti- 

 ation of the more peripheral part (exoplasm) of the young connective tissue 

 cells, the fibroblasts, which in the earliest stages are united in a common 

 cytoplastic reticulum or syncytium. To the agency of the cells, then, must 

 be ascribed the production of the fibrous intercellular substance. 



The white fibres are grouped in more or less definite bundles, which, 

 as seen in the usual teased preparations of areolar tissue, exhibit a wavy 

 longitudinal striation. This marking is due to the apposition of the individ- 

 ual fibrillae, which are so thin as to have no appreciable width. In the 

 denser forms of fibrous tissue, as in tendon, the white fibres are assembled 

 in robust fasciculi with great regularity and so closely packed and luted 

 together by cement-substance that all trace of the individual fibrillse is lost, 

 the bundle appearing homogeneous, unless some means is taken to dissoci- 

 ate its component fibrils. White fibres yield gelatin on boiling with water, 

 and consist chemically of an albuminoid substance termed collagen. They 

 are not digested by pancreatin and on the addition of acetic acid become 

 swollen and transparent and, finally, invisible. 



