722 



FAT-CELLS. 



Fig 



gated in distinct masses, constituting the proper Adipose tissue. 

 The individual Fat-cells always present a nearly spherical or sphe- 

 roidal form; sometimes, however, when they are closely pressed 

 together, they become somewhat polyhedral, from the flattening of 

 their walls against each other (Fig. 383). Their intervals are tra- 

 versed by a minute network of 

 Blood-vessels (Fig. 395), from which 

 they derive their secretion ; and it 

 is probably by the constant moisten- 

 ing of their walls with a watery 

 fluid, that their contents are re- 

 tained without the least transuda- 

 tion, although these are quite fluid 

 at the temperature of the living 

 body. Fat-cells, when filled with 

 their characteristic contents, have 

 the peculiar appearance which has 

 been already described as apper- 

 taining to Oil-globules (§ 129), being 

 very bright in their centre, and very 

 dark towards their margin, in con- 

 sequence of their high refractive 

 power ; but if, as often happens in 

 Areolar and Adipose tissue ; preparations that have been long 

 a, a, fat-cells; b, b, fibres of mounted, the oily contents should 

 areolar tissue. have escaped, they then look like any 



other cellsof the sameform. Although 

 the fatty matter which fills these cells (consisting of a solution of 

 Stearine or Margarine in Oleine) is liquid at the ordinary tem- 

 perature of the body of a warm-blooded animal, yet its harder 

 portion sometimes crystallizes on cooling ; the crystals shooting 

 from a centre, so as to form a star-shaped cluster. — In examining 

 the structure of Adipose tissue, it is desirable, where practicable, 

 to have recourse to some specimen in which the Fat-cells lie in 

 single layers, and in which they can be observed without disturb- 

 ing or laying them open; such a condition is found, for example, 

 in the mesentery of the Mouse ; and it is also occasionally met 

 with in the fat-deposits which present themselves at intervals in 

 the Connective tissues of the muscles, joints, &c Small collec- 

 tions of Fat-cells exist in the deeper layers of the True Skin, and 

 are brought into view by vertical sections of it (Fig. 378, /). And 

 the structure of large masses of Fat may be examined by thin 

 sections, these being placed under water in thin cells, so as to 

 take-off the pressure of the glass-cover from their surface, which 

 would cause the escape of the oil-particles. No method of mount- 

 ing (so far as the Author is aware) is successful in causing these 

 Cells permanently to retain their contents. 



565. Cartilage. — In the ordinary forms of Cartilage, also, we 



