38 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



or smaller quantity of adipose or fatty tissue is present. Adipose tissue is 

 almost always found seated in areolar tissue, and forms in its meshes little 

 masses of unequal size and irregular shape, to which the term lobules is com- 

 monly applied. 



Structure. Adipose tissue consists essentially of cells which present 

 dark, sharply defined edges when viewed with transmitted light; each con- 

 sisting of a structureless and colorless membrane or bag formed of the re- 

 mains of the original protoplasm of the cell, filled with fat. A nucleus 



FIG. 45. A Lobule of Developing 

 Adipose Tissue from an Eight-months 

 Fetus, a, Spherical or, from pressure, 

 polyhedral cells with large central nu- 

 cleus, surrounded by a finely reticulated 

 substance staining uniformly with hema- 

 toxylin. b, Similar cells with spaces 

 from which the fat has been removed 

 by oil of cloves, c, Similar cells showing 

 how the nucleus with enclosing proto- 

 plasm is being pressed toward periphery. 

 d, Nucleus of cndothelium of investing 

 capillaries. (McCarthy.) Drawn by 

 Treves. 



FIG. 46. Branched Connective- 

 tissue Corpuscles, Developing 

 into Fat Cells. (Klein.) 



is always present in some part or other of the cell protoplasm, but in the 

 ordinary condition of the loaded cell it is not easily or always visible. This 

 membrane and the nucleus can generally be brought into view by extracting 

 the fat with ether and by staining the tissue. 



The ultimate cells are held together by capillary blood vessels, figure 44; 

 while the little clusters thus formed are grouped into small masses, and 

 held so, in most cases, by areolar tissue. The oily matter contained in the 

 cells is composed chiefly of the compounds of fatty acids with gylcerin, olein, 

 stearin, and palmitin. 



Development of Adipose Tissue. Fat cells are developed from connective- 

 tissue corpuscles. In the infra-orbital connective tissue there are cells ex- 



