36 HAND-BOOK OF PHYSIOLOGY. 



Fatty matter, not in the form of a distinct tissue, is also widely pres- 

 ent in the body, e.g., in the liver and brain, and in the blood and chyle. 



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 commonly applied. 



Structure. Under the microscope adipose tissue is found to consist 

 essentially of little vesicles or cells which present dark, sharply-defined 

 edges when viewed with transmitted light: they are about j-J-g- or ^ w of 

 an inch in diameter, each composed of a structureless and colorless mem- 

 brane or bag, filled with fatty matter, which is liquid during life, but in 

 part solidified after death (Fig. 34). A nucleus is always present in some 

 part or other of the cell- wall, but in the ordinary condition of the cell it 

 is not easily or always visible. 



FIG. 34. FIG. 35. 



FIG. 34. Ordinary fat-cells of a fat tract in the omentum of a rat. (Klein.) 

 FIG. 33. Group of fat-cells (TO) with capillary vessels (c). (Noble Smith.) 



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

 staining the tissue: it can be still more satisfactorily demonstrated by ex- 

 tracting the contents of the fat-cells with, ether, when the shrunken, 

 shriveled membranes remain behind. By mutual pressure, fat-cells come 

 to assume a polyhedral figure (Fig. 35). 



The ultimate cells are held together by capillary blood-vessels (Fig. 

 35); 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 com- 

 pounds of fatty acids with glycerin, which are named olein, stearin, and 

 palmitin. 



Development of Adipose Tissue. Fat-cells are developed from 

 connective- tissue corpuscles: in the infra-orbital connective-tissue cells 

 may be found exhibiting every intermediate gradation between an ordi- 

 nary branched connective-tissue corpuscle and a mature fat-cell. The 

 process of development is as follows: a few small drops of oil make their 



