34 THE ESSENTIALS OF HISTOLOGY 



The branched cells and cell-spaces of areolar tissue come into 

 intimate relation with the cells lining the lymphatic vessels and small 

 blood-vessels. This connection can best be seen in silvered prepara- 

 tions ; it will be again referred to in speaking of the origin of the 

 lymphatics. 



Adipose tissue consists of vesicles filled with fat (fig. 36), and col- 

 lected into lobules or into tracts which accompany the small blood- 

 vessels. The vesicles are round or oval in shape, except where closely 

 packed, when they become polyhedral from mutual compression. The 

 fat-drop is contained within a delicate protoplasmic envelope (fig. 36, 

 m) which is thickened at one part, and here includes an oval flattened 

 nucleus. The vesicles are supported partly by filaments of areolar 

 tissue, but chiefly by a fine network of capillary blood-vessels. 



The fat when first formed is deposited within plasma-cells of areolar 

 tissue (fig. 37). It is at first in separate droplets within each cell, but 



FIG. 37. DEPOSITION of FAT IN CONNECTIVE-TISSUE CKLI,S. 



/, a cell with a few isolated fat-droplets In its protoplasm ; /', a cell with a single large and 

 several minute drops ; /", fusion of two large drops ; g, granular or plasma cell, not 

 yet exhibiting any fat-deposition ; c t, flat connective-tissue corpuscle ; c, c, network of 

 capillaries. 



as these droplets increase in size they run together into a larger drop, 

 which gradually fills the cell more and more, swelling it out so that 

 the cell -protoplasm eventually appears merely as the envelope of the 

 fat-vesicle. 



Fat is found most abundantly in subcutaneous areolar tissue, and 

 under the serous membranes ; especially in some parts, as at the back 

 of the peritoneum around the kidneys, under the epicardium, and in 

 the mesentery and omentum. The marrow of the long bones is also 

 principally composed of fat. 



