SEC. 6. THE HISTOKY OF FAT. ADIPOSE TISSUE. 



396. Globules of fat of various sizes make their appear- 

 ance in the very elements of most of the tissues, in muscular 

 fibres, in epithelial cells, in nerve cells, in leucocytes, and so on ; 

 and the medulla of medullated nerves consists largely of a 

 peculiar fatty material. Besides this, certain cells of connec- 

 tive tissue at various times, and in various places, become so 

 loaded with fat that groups of the cells become practically 

 masses of fat. Connective tissue thus loaded with fat is called 

 adipose tissue ; and masses of adipose tissue of all manner of 

 sizes and of shapes adapted to the several situations are found 

 in various parts of the body. Many of the internal organs, 

 more especially the kidneys, are wrapped in adipose tissue ; but 

 the largest deposit is one lying in the subcutaneous connective 

 tissue, sometimes called the "panniculus adiposus ; " and a 

 4 fat ' body is distinguished from a ' lean ' body chiefly, though 

 by no means exclusively, by the amount of subcutaneous adi- 

 pose tissue. 



Of all the tissues of the body adipose tissue is the most 

 fluctuating in bulk ; within a very short space of time a large 

 amount of adipose tissue may disappear, and within a very short 

 space of time the quantity present in a body may be several 

 times multiplied. When too much or too little food is given it 

 is the subcutaneous adipose tissue which first and most rapidly 

 increases or decreases in bulk. 



397. A fat-cell is a cell, belonging to connective tissue, 

 in the cell-substance of which fat has been collected to such an 

 extent that the cell, which increases largely in bulk during the 

 process, is almost wholly transformed into a large vacuole filled 

 with fat, the cell -substance being reduced to a thin envelope of 

 the vacuole, thickened at one part where the nucleus, thrust on 

 one side by the gathering fat, is placed. Adipose tissue is a 

 collection of such fat-cells held together by a meagre quantity 

 of vascular connective tissue. 



By studying the development of adipose tissue in the embryo 

 or elsewhere, we may trace out the steps of the formation of the 



604 



