ADIPOSE TISSUE. 



sited beneath the serous membranes, or is collected between their folds, as in 

 the mesentery and omentum, at first generally gathering along the course of 

 the blood-vessels, and at length accumulating very copiously. Collections 

 of fat are also common round the joints, lying on the outer surface of the 

 synovial membrane, and filling up inequalities ; in many cases lodged, like 

 the fat of the omentum, in folds of the membrane, which project into the 

 articular cavity. Lastly, the fat exists in large quantity within the bones, 

 where it forms the marrow. On the other hand, there are some parts in 

 which fat is never found in the healthy condition of the body. Thus it 

 does not exist in the subcutaneous areolar tissue of the eyelids and penis, 

 nor in the lungs, nor within the cavity of the cranium. 



When subjected to the 



Fig. XXXIV. microscope, the adipose 



tissue (fig. xxxiv.) ia 

 seen to consist of small 

 vesicles, filled with an 

 oily matter, and for the 

 most part lodged in the 

 meshes of the areolar 

 tissue. The vesicles are 

 most commonly collected 

 into little lobular clusters, 

 and these again into the 

 little lumps of fat which 

 we see with the naked 

 eye, and which in some 

 parts are aggregated into 

 round or irregular masses 

 of considerable magni- 

 tude. Sometimes the vesicles, though grouped together, have less of a clus- 

 tered arrangement ; as when they collect alongside of the minute blood- 

 vessels of thin membranous parts. 



In well-nourished bodies the vesicles or fat- cells are round or oval, unless 

 where packed closely together, in which case they acquire an angular figure, 

 and bear a striking resemblance to the cells of vegetable tissues. The 

 greater number of them are from 3-^3 th to ^gth ^ an i QCn i Q diameter, 

 but many exceed or fall short of this measurement. Each one consists of a 

 very delicate envelope, inclosing the oily matter, which, completely filling 

 the envelope, appears as a single drop. The envelope is generally quite 

 transparent, and apparently homogeneous in structure. In ill-nourished 

 bodies, and especially in those presenting serous infiltration of the tissues 

 (as in dropsy), different forms of fat cells are observed. (1.) Granular, 

 yellowish- white vesicles, containing numerous small fat-globules. (2.) 

 Yellow, or yellowish-red cells, filled with serum and globules of browni*h- 

 yellow fat. The relative proportion of the serum and fat varies ; but in all 

 cases of this description Kolliker states that he has discovered a nucleus and 

 a nucleolus. The nucleus may be seen without re-agents, but is rendered 

 more apparent by acetic acid. The vesicular envelope is found in different 

 conditions. Sometimes it is normal ; but it has been seen finer and also 

 thicker than usual. When thickened, it may present the appearance of 

 either a single or a double contour. (3.) Fatless cells, with normal or 

 thickened walls. (4.) Fat- cells containing crystals (probably of margaric 

 acid), either yellow or white in colour. At first sight these cells appear filled 



Fig. 



XXXIV. A SMALL CLUSTER OP FAT-CELLS J MAG- 

 NIFIED 150 DIAMETERS. 



