OP THE PURELY CELLULAR TISSUES. FAT. 



257 



are dispersed among the interspaces of Areolar tissue, in most, but not all, of 

 the situations in which the latter presents itself; but there are certain situa- 



Fig. 48. 



Fig. 49. 



Cells of Adipose Tissue. Magnified 135 diameters. Fat vesicles assuming the polyhedral 



form from pressure against one another. 

 The capillary vessels are not represented. 

 From the omentum; magnified about 

 300 diameters. 



tions in which they are developed more abundantly, filling up interstices, and 

 forming a pad or tissue for the support of movable parts. In all but very 

 emaciated individuals, there is a considerable amount of fat beneath the skin; 

 and it is in great part to its interposition, that the roundness and smoothness of 

 the surface, especially in the female, are due. But fat is collected in large 

 quantities around certain internal organs, as the kidneys, where its use is less 

 obvious ; and here, as well as at the base of the heart around the origin of the 

 large vessels, in the orbit of the eye, in the interior of the bones, and within 

 the spinal canal between the periosteum and the dura mater, some fat is always 

 left, however extreme may be the general emaciation. The diameter of the 

 greater number of Fat-cells is between l-300th and l-600th of an inch, but 

 larger and smaller sizes are frequently to be met with. The nucleus is seldom to 

 be distinguished in the fully-developed fat-cell ; but it is probable that it has not 

 ceased to exist there, but is simply obscured by the oily cell-contents. For not 

 only does a nucleus exist in the fat-cells of the embryo, which are at first pel- 

 lucid vesicles, then become granular, and at last acquire oily contents ; and also 

 in the rudimentary fat-cells closely resembling these in their successive stages, 

 which are described by Prof. Kolliker as existing in the Dartos; but also in 

 fat-cells wholly deprived of their oily contents, which are not unfrequently met 

 with in emaciated or dropsical subjects. When the fat-cells are aggregated so 

 as to form masses of Fat, they are first collected into little lobular clusters, each 

 of which has a delicate membranous investment ; and these are again united 

 into larger clusters, visible to the naked eye, whose further aggregation may 

 form masses of considerable size. The component parts of these are held 

 together by Areolar tissue, and also by the bloodvessels which penetrate them, 

 and which ramify minutely among them, forming a capillary network, not only 

 upon the surface of the smallest lobules, but even (it would appear) between 

 their contained fat-cells (Fig. 50). In some forms of Adipose tissue, such as 

 the marrow of bones, it would seem that very little areolar tissue exists, or 

 that it is even entirely absent ; and here the capillary plexus forms the princi- 

 pal bond of union between the fat-cells. No lymphatics have been detected in 

 Adipose tissue ; and it would seem to be equally destitute of nerves, excepting 

 of such as are passing through it on their way to other textures ; thus account- 

 17 



