FAT CELLS. 43 



on boiling. Because of the difference in chemical composition, elastic 

 fibers may be stained with dyes which fail to color white fibers: thus 

 resorcin-fuchsin stains them dark purple, but scarcely affects the white 

 fibers; on the other hand, Mallory's connective tissue stain makes the 

 white fibers deep blue, the elastic elements remaining colorless or pale 

 pink. These special stains are of the greatest importance in studying 

 connective tissue. In ordinary specimens white fibers appear blended 

 in masses and the small elastic fibers are invisible. There may be other 

 sorts of fibers than the white and elastic, such as the fibroglia of Prof. 

 Mallory, but these are still very little understood. 



Cells. Usually the cells of connective tissue are conspicuous only 

 through their flattened nuclei, which are broadly elliptical on surface 

 view, and rod shaped when seen on edge. The protoplasm forms a wide, 

 thin layer, and since it is closely applied to the fiber bundles which it may 

 encircle, and ordinarily stains like them, very 

 often it can scarcely be distinguished. As a 

 whole, the cells are irregularly polygonal, flat- 

 tened, and bent to confom with the fibers. In 

 some lamellar tissues these flat cells are in con- 

 tact with one another along their edges, thus 

 simulating an epithelium. In loose connective 

 tissue they may be widely separated. They 

 possess processes which may or may not unite 

 with those from other cells, and in their proto- FlG - N 4 E 4 o7 s D Fl? L c P ELLs SU HUMA A N 

 plasmic bodies there are often a few small fat / ETUS / FlvE MoNT f- 



n., Nucleus; f. v., fat vacuole; p. r., 

 droplets. protoplasmic rim. 



Fat cells, as may be seen in the subcutaneous tissue of a five months' 

 fetus (Fig. 44) arise from mesenchymal cells by the development of 

 vacuoles of fat within their protoplasm. The vacuoles enlarge and coalesce, 

 so that the nucleus is crowded to one side, lying in a rim of unaltered 

 protoplasm. Gradually the protoplasmic processes disappear. The re- 

 sulting form of cell has often been compared with a "signet ring," referring 

 to its appearance when seen in section. The vacuole of fat further enlarges 

 so that the nucleus is flattened and the protoplasmic layer becomes very 

 thin. In fresh cells it cannot be seen. The entire structure appears as a 

 large refractive drop of oil, Fig. 41, spheroidal if occurring singly, or 

 polyhedral if compressed by adjoining cells. Small fat drops may be 

 scattered through the specimen due to rupture of the cells. In order to 

 study fat in sections it is necessary to employ special reagents. The tissue 

 may be preserved either in osmic acid which blackens the fat, or in a 

 formalin solution and afterwards stained with Sudan III or Sharlach R, 



