GO 



CONNECTIVE TISSUE. 



iu the healthy condition of the body. Thus it does not exist in the sub- 

 cutaneous areolar tissue of the eyelids and i^euis, nor in the lungs, 

 nor within the cavity of the cranium. 



Structure. — When subjected to the microscope, the adipose tissue 

 (fig. 33) is seen to consist of small vesicles, tilled with an oily matter, 

 and for the most part lodged in the meshes of tlie 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 magnitude. Sometimes the vesicles, though grouped 

 together, have less of a clustered 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 

 Avhich case they acquire an angular figure, 

 and bear a striking resemblance to the cells 

 of ve2;etable tissues. The o'reater number of 



Fie. 34. 



them 



are from -r^th to g^th of an inch 



in 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 enve- 

 lope, appears as a single drop. 



A nucleus is commonly present (fig. 34), 

 but is usually obscured by the fatty matter. 

 The envelope is the remains of the original 

 protoplasm of the cmbrj'onic cell : it is gen- 

 erally quite transparent and apparently 

 homogeneous in structure. According to 

 some EtLithorities it consists of two parts, 

 a delicate structureless external membrane, 

 and a layer of finely granular protoplasm 

 immediately surrounding the fat. 



ig. 34. — Fat Cells from 

 Rabbits' Omentum, showing 

 Nucleus and Pkotoplasmic 

 Envelope, avith supporting 

 Areolar Tissue between 

 the Cells (Kleiii). 



Such is the normal condition, but in emaciated, dropsical, and old persons, the 

 oily contents of the cells may become wholly or partially removed, in which case 

 serous fluid may be found occupying its place, and then too the nucleus becomes 

 apparent. 



The common fat of the human body consists essentially of palmitm, steai-in 

 and olein, which are the compounds of glycerine with palmitic, stearic and oleic 

 acids respectively. These compounds, which are considered to be glycerine- 

 ethers, contain three equivalents of the fatty acid to each equivalent of glyce- 

 rine ; they have hence been termed tri-palmitin, tri-stearin, and tri-olein. 

 The tri-olein, or liquid fat, holds the other two in solution : and the varying 

 consistency of animal fats depends on the relative proportion of the solid and 

 liquid ingredients. Dm'ing life the oily matter contained in the cells is liquid ; 

 but the acicular crystalline spots whicli are sometimes seen after death indicate 

 a partial solidification of one of its constituents. 



The fat being thus contained in closed cells, it will be readily understood why, 

 though liquid or nearly so in the living Ijody, it does not sliift its place in 

 obedience to pressure or gTavitation. as happens with the water of dropsy and 

 other fluids effused into the interstices of the areolar tissue : such fluids, being 

 uncoufined, of course readily pass from one place to another through the open 

 meshes. 



The areolar tissue connects and surrounds the larger lumps of fixt. 



