THE STRUCTURE OF THE ELEMENTARY TISSUES. 49 



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 ^ or -^ of 

 an inch in diameter, each consisting of a structureless and colorless 

 membrane or bag formed of the remains of the original protoplasm of 

 the cell, filled with fatty matter, which is liquid during life, but in part 

 solidified after death (fig. 48). A nucleus is always present in some part 

 or other of the cell-protoplasm, but in the ordinary condition of the cell 

 it is not easily or always visible (fig. 49). 



This membrane and the nucleus can generally be brought into view 

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

 by extracting the contents of the fat-cells with ether, when the shrunken, 

 shrivelled membranes remain behind. By mutual pressure, fat-cells 



9 

 Fig. 49. Group of fat cells (F c) with capillary vessels (c). (Noble Smith.) 



come to assume a polyhedral figure (fig. 49). When stained with osmic 

 acid fat-cells appear black. 



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

 50); 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 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 mature fat-cell. The 

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

 appearance in the protoplasm and by their confluence a larger drop is 

 produced (fig. 51) : this gradually increases in size at the expense of the 

 original protoplasm of the cell, which becomes correspondingly dimin- 

 ished in quantity till in the mature cell it only forms a thin crescentie 

 4 



