CONNECTIVE TISSUE. 



respectively. In the dense forms of connective tissue the fiber-bundles 

 tend to be parallel and are closely packed. In loose or areolar connective 

 tissue the fibers run in various directions, and among them are cells which 

 have become charged with fat. When these are numerous they constitute 

 fat tissue (adipose tissue). Areolar connective tissue ordinarily contains 

 fat cells. In every specimen of connective tissue three features should 

 be examined: the fibers, the cells, and the remains of the intercellular 

 substance. 



Fibers. If a small piece of fresh connective tissue, such as envelops 

 the muscles of a guinea pig, be pulled apart on a slide and examined in 

 water, it will exhibit the structures shown in Fig. 41. Most of the specimen 

 may be obscure, but in such parts as were properly spread out the ichitc 

 fibers can be seen as pale, wavy 

 bands, without sharp borders. 

 They are faintly striated longi- 

 tudinally, due to the fact that 

 they are bundles of minute 

 fibrils bound together by a 

 small amount of cement sub- 

 stance. The addition of picric 

 acid causes them to separate 

 into their constituent elements. 

 The white fibers divide, as 

 shown in the figure, by the 

 separation of the fibrils into 

 smaller groups; the fibrils 

 themselves do not branch. If 

 dilute acetic acid is put upon 

 the specimen, these fibers swell, 



as shown in Fig. 41, B, often presenting a series of constrictions ascribed 

 to the remains of encircling cells, to rings of elastic fiber, or to remnants of 

 a sheath which enveloped the bundle. Ultimately the white fibers disap- 

 pear in acids or in alkalies. Chemically they are said to consist of collagen, 

 an albuminoid body which on boiling yields gelatin (glutin, the source of 

 glue). The white fibers are supposed to arise in the exoplasm. Those 

 seen in mucous tissue were of this variety. 



Elastic fibers are probably always present in connective tissue, though 

 varying greatly in their abundance. They are said to develop later than 

 the white fibers and are absent from corneal tissue, mucous tissue, and 

 generally, though not always, from reticular tissue. In Fig. 41 they are 

 seen as sharply defined, straight or stiffly bent, homogeneous structures 



Fat Cell 



Wh.F. 



FIG. 41. FRESH CONNECTIVE TISSUE FROM AROUND THE 



SHOULDER MUSCLES OF A GUINEA PIG. 

 A, Before and B, after adding dilute acetic acid. El. F., 



Elastic fiber; Wh. F., white fiber; n., nucleus of 



connective tissue cell. 



