SEC. 7. THE HISTORY OF FAT. ADIPOSE TISSUE. 



502. 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 connective 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, 432, sometimes called the 

 " panniculus adiposus " ; and a ' fat ' body is distinguished from a 

 ' lean ' body chiefly, though by no means exclusively, by the 

 amount of subcutaneous adipose tissue. 



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

 ating in bulk; within a very short space of time a large amount of 

 adipose tissue may disappear, and within an almost equally short 

 time the quantity present in a body may be several times multi- 

 plied. When too much or too little food is given it is the subcu- 

 taneous adipose tissue which first and most rapidly increases or 

 decreases in bulk. 



503. A small piece of adipose tissue, examined under a low 

 power, appears to be made up almost entirely of rounded masses 

 of highly refractive material, closely packed together. These 

 rounded masses, which stain an intense black with osmic acid and 

 give other reactions of fat, are arranged in irregular lobules ; 

 between the lobules, and between the individual rounded masses, 

 may be seen a small amount of fibrillated connective tissue 

 carrying blood vessels. 



When the tissue has been hardened and stained, and the fat 

 has been removed by solvents, what was previously only visible as 



F. 49 



