8o HUMAN ANATOMY. 



tissue does not occur even when developed to excess in other parts. As ordinarily 

 seen, adipose tissue is of a light straw color and often presents a granular texture 

 due to the groups of fat-cells within the supporting areolar tissue. 



Examined microscopically in localities where the fat-cells are not crowded, but 

 occur in a single stratum and hence retain their individual form, adipose tissue is 

 seen to be made up of relatively large, clear, spherical sacs held together by deli- 

 cate areolar tissue. Unless treated with some stain, as osmic acid, Sudan III. or 

 quinoline-blue, possessing an especial afifinity for fat, the oily contents of the cells 

 appear transparent and uncolored, and apparently occupy the entire cell-body. 

 Critical study of the fat-cell, however, demonstrates the presence of an extremely 

 thin enveloping layer of protoplasm, a local thickening on one side of the sac mark- 

 ing the position of the displaced and compressed nucleus (Fig. 109). 



Fat-cells occur usually in groups, supported and held together by highly vas- 

 cular connective tissue. In localities possessing considerable masses of fat, as be- 

 neath the scalp and the skin, the cells are grouped into lobules which appear as 

 yellow granules to the unaided eye ; in such localities the typical spherical shape of 

 the individual fat-cells is modified to a polyhedral form as the result of the mutual 

 pressure of the closely packed vesicles. 



In connective-tissue elements about to become fat-cells, isolated minute oil- 

 drops first appear within the protoplasm ; these increase in size, coalesce, and grad- 

 ually encroach upon the cytoplasm until the latter is reduced to a thin, almost 

 inappreciable, envelope, which invests the huge distending oil-drop. The nucleus, 

 likewise, is displaced towards the periphery, where it appears in profile as an incon- 

 spicuous crescent embedded within the protoplasmic zone. After the disappearance 

 of the fatty matters, as during starvation, the majority of fat-cells are capable of 

 resuming the usual appearance and properties of connective-tissue corpuscles ; cer- 

 tain groups of cells, the fat-oi^gans of Toldt, however, exhibit an especial tendency 

 to form adipose tissue, and hence only under exceptional conditions part with their 

 oily contents. 



CARTILAGE. 



Cartilage includes a class of connective tissue in which the intercellular substance 

 undergoes increasing condensation until, as in the hyaline variety, the intercellular 

 matrix appears homogeneous, the constituent fibres being so closely blended that 

 the fibrous structure is ordinarily no longer appreciable. 



Depending upon the differences presented by the intercellular matrix, three 

 varieties of cartilage are recognized, — hyaline, elastic, zxi<\ fibrous. Considered in 

 relation to the denser connective tissues, the description of fibrous cartilage, which 

 differs but little from white fibrous tissue, should next follow ; since, however, the 

 term "cartilage" is usually applied to the hyaline variety, the latter will first claim 

 attention. 



Hyaline cartilage, or gristle (Fig. no), enjoys a wide distribution, forming 

 the articular surfaces of the bones, the costal cartilages, the larger cartilages of the 

 larynx and the cartilaginous plates of the trachea and bronchi, the cartilages of the 

 nose and part of the Eustachian tube. In the embryo the entire skeleton, with the 

 exception of part of the skull, is mapped out by primary hyaline cartilage. 



The apparently homogeneous matrix of hyaline cartilage, after appropriate 

 treatment, is resolvable into bundles of fibrous tissue ; ordinarily, however, these are 

 so closely united and blended by the cementing ground-substance that the presence 

 of the component fibrils is not evident. 



The cartilage-cells, as the connective-tissue elements which lie embedded within 

 the hyaline matrix are called, are irregularly oval or spherical, nucleated bodies. 

 They occupy more or less completely the interfascicular clefts, or lactincB, within 

 which they are lodged. In adult tissue usually two or more cells share the same 

 compartment, the group representing the descendants from the original occupant of 

 the space. The matrix immediately surrounding the lacunae is specialized as a layer 

 of different density, and is often described as a capsule ; a further differentiation 

 of the ground-substance is presented by the more recently formed matrix, which 



