ADIPOSE TISSUE. 



237 



consists of two parts, a delicate structureless external membrane, and a layer of 

 finely granular protoplasm immediately surrounding the fat. The nucleus (ri) is 

 always present in the protoplasm, but is often so flattened out by the pressure of the 

 inclosed oil-drop as to be visible only with difficulty. 



The areolar tissue connects and surrounds the larger lumps of fat, but forms no 

 special envelope to the smaller clusters ; and although fine fasciculi and filaments of 

 that tissue pass irregularly over and through the clusters, yet it is probable that the 

 vesicles are held together in these groups mainly by the fine network of capillary 

 vessels distributed to them. In the marrow the connective tissue fibrils are but few 

 in number or may, it is said, be absent altogether. 



The adipose tissue is copiously supplied with blood-vessels. The larger 

 branches of these pass into the fat-lumps, where they run between the lobules and 



Fig. 277. DEPOSITION OF FAT IN CONNECTIVE TISSUE CELLS 



OF THE NEW-BORN KAT. (E. A. S. ) 



/, /', fat-cells ; h, hsemapoietic cell. 



subdivide, till at length a little artery and vein 



are sent to each small lobule (fig. 275, a, v), 



dividing into a network of capillary vessels, 



which pass between the vesicles in all directions, 



supporting and connecting them. The lymphatics of the fat are in close relation 



to the blood-vessels, accompanying and occasionally completely enclosing them as 



they enter the lobule. No nerves have been seen to terminate in this tissue, although 



J 



Fig. 278. DEPOSITION OF FAT IN CON- 

 NECTIVE TISSUE CELLS. (E. A. S.) 



/, a cell with a few isolated fat- 

 droplets in its protoplasm ; /', a cell 

 with a single large and several minute 

 drops ; /", fusion of two large drops ; 

 (/, granular cell, not yet exhibiting 

 any fat deposition ; c t, flat connective 

 tissue corpuscle ; c, c, network of 

 capillaries. 



nerves destined for other tex- 

 tures may pass through it. 

 Accordingly it has been ob- 

 served that, unless when such 

 traversing nervous twigs hap- 

 pen to be encountered, a puncturing instrument may be earned through the adipose 

 tissue without occasioning pain. 



Development. The fat first appears in the human embryo about the fourteenth 

 week of intra-uterine life. It is deposited in the form of minute granules or drop- 

 lets in certain cells of the connective tissue (figs. 277, 278, /, /): these droplets 

 increase in size, and eventually run together, so as to form one large drop in each 

 cell. By further deposition the cell becomes swollen out to a size far beyond that 

 which it possessed originally, and its protoplasm remains as a delicate envelope 

 surrounding the fat-drop. By the end of the fifth month the fat-cells have largely 

 increased in number, and have become collected into small groups. 



The deposit of fat within the cells is preceded and accompanied by the formation 

 of a rich network of capillary blood-vessels (fig. 278), which are produced by a 

 transformation of other cells of the tissue in the manner previously described 

 (p. 218). 



The fat is often deposited in the granular cells of the connective tissue, these 



R 2 



