468 



OF NUTRITION. 



number of rounded granules, which, when separately viewed, are found to be 

 transparent, not black and opaque ; these granules are flat oval corpuscles, 

 measuring about l-20,000th of an inch in diameter, and about a quarter as 

 much in thickness ; they exhibit a very active molecular movement when set 

 free by the bursting of the cell, and this has even been noticed while they are 

 enclosed. The chemical nature of the black pigment has not yet been made 

 evident ; it has been shown, however, to have a close relation to that of the 

 Cuttle-fish ink (which derives its colour from pigment-cells lining the ink-bag) ; 

 and to contain a larger proportion of Carbon than most other organic sub- 

 stances, every 100 parts containing 58<| of this element. The nucleus of 

 the pigment cells may generally be traced as a clear spot. 



618. The Fat-cells, of which Adipose tissue is composed, also permanently 

 exhibit the original type of structure in its simplest form. This tissue is usually 

 diffused over the whole body, filling up interstices, and forming a kind of pad 

 or cushion for the support of movable parts. Even in cases of great ema- 

 ciation, some Fat is always left ; especially at the base of the heart, around the 

 origin of the large vessels ; in the orbit of the eye ; in the neighbourhood of 

 the kidney; in the interior of the bones ; and within the spinal canal, between 

 the periosteum and the dura mater. The Fat Cells are usually spherical or 

 spheroidal ; sometimes, however, when closely pressed together without the 

 intervention of any intercellular substance, they become polyhedral. The 

 nucleus is not always to be distinguished ; perhaps in consequence of its 

 having passed to the interior of the cell. 



[The Fat-cell is composed of the adipose tissue, a closed vesicle formed by a membrane 

 of extreme tenuity, and the material which it contains, ihefat. The membrane is per- 

 fectly homogeneous and transparent, about the 2 <j<J<yflth of an inch thick, and is moistened 

 by a watery fluid, for which it has a greater attraction than the fat it contains. Each 

 vesicle is a perfect organ, from Tj^th to ^^th of an inch in diameter, with capillaries 



Fig. 104. 



Fig. 105. 



Fat vesicles, assuming the poly- 

 hedral form from pressure against 

 one another. The capillary vessels 

 are not represented. From the 

 omentum ; magnified about 300 dia- 

 meters. 



Blood-Vessels of Fat ; 1, minute flattened fat-lobule, in which 

 the vessels only are represented; 3, the terminal artery; 4, the 

 primitive vein ; 5, the fat vesicles of one border of the lobule, 

 separately represented, magnified 100 diameters; 2, plan of the 

 arrangement of the capillaries on the exterior of the vesicles, 

 more highly magnified. 



