3& CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



Structure. Adipose tissue consists essentially of cells which present 

 dark, sharply denned 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 

 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. 



FIG. 44. Blood Vessels of Adipose Tissue. A, Minute flattened fat lobule, in which 

 the vessels only are represented, a, The terminal artery; v, the primitive vein; b, the fat 

 vesicles of one border of the lobule separately represented. X 100. B, Plan of the 

 arrangement of the capillaries, c, On the exterior of the vesicles; more high y magnified. 

 (Todd and Bowman.) 



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- 

 hibiting every intermediate gradation between an ordinary branched connect- 

 ive-tissue corpuscle and mature fat cells. Their developmental appearance 

 is as follows: a few small drops of oil make their appearance in the proto- 

 plasm, and by their confluence a larger drop is produced, figure 45. This 

 gradually increases in size at the expense of the original protoplasm of the 

 cell, which becomes correspondingly diminished in quantity till in the mature 

 cell it forms only a thin crescentic film with a nucleus closely pressed against 

 the cell wall. Under certain circumstances this process may be reversed. 



A large number of blood vessels are developed in adipose tissue, which 



