770 STRUCTURE OF ADIPOSE TISSUE. [BOOK n. 



a rounded mass of fat is now seen, under higher powers, to be 

 ; a cell, but a cell nearly the whole of the cell-substance of which 

 has become transformed into a single large vacuole. Over the 

 greater part of the circumference of the cell the cell-substance is 

 reduced to a mere thin shell or envelope, or cell-membrane, but 

 at one part a thicker disc-like remnant is seen, and in this is 

 placed a rounded or oval, often flattened nucleus. Between these 

 fat-cells may be seen a few bundles of connective tissue forming a 

 scanty loose network, the rounded meshes of which are occupied 

 by the fat-cells, the matrix of the bundles appearing at places 

 continuous with, or adherent to, the envelopes of the cells ; 

 ordinary connective tissue corpuscles are also here and there 

 present, though rarely visible between the larger, 50/t to 130^, 

 fat-cells. In injected specimens it is further seen that the con- 

 nective tissue meshwork carries small blood vessels, which form 

 capillary networks round the groups of fat-cells and even round 

 individual cells. After death, upon cooling, the fat in the fat-cells 

 may solidify in crystals. 



It is obvious that 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 

 fat-cells. In the embryo, in a situation where adipose tissue is 

 about to be formed, the connective tissue is seen to contain a 

 number of small nucleated cells, rounded or somewhat irregular in 

 form, the cell- substance of which at first presents no special 

 characters, and contains not more than what may be called the 

 ordinary amount of fat globules or spherules. Very soon however 

 these minute drops or specks increase in number, the cell- 

 substance at the same time increasing in bulk while remaining 

 round or becoming more distinctly so, and the smaller drops run 

 together into larger ones. This goes on ; the fat increasing in 

 quantity coalesces more and more, and the cell, as a whole, 

 becomes larger and larger, the cell-substance at first keeping up 

 in bulk with the increasing fat, but subsequently ceasing to 

 increase, being apparently used up in the formation of the fat. 

 Thus the original small ' protoplasmic ' cell is at last transformed 

 into the larger fat-cell, all the fat having run together into a 

 vesicle the envelope of which, thickened on one side to carry the 

 nucleus, is furnished by the remnant of the cell-substance. In 

 some cases, the nucleus instead of being pushed early on one 



