34 HUMAN PHYSIOLOGY. 



In the embryonic state the elements of this form of connective tissue are 

 united by a ground substance, gelatinous in character. In the adult state 

 this substance shrinks and largely disappears, leaving intercommunicating 

 spaces of varying size and shape, from which the tissue takes its name. When 

 subjected to the action of various reagents, and examined microscopically, 

 the bundles can be shown to consist of extremely delicate, colorless, trans- 

 parent, wavy fibers, which are cemented together by a ground substance 

 composed largely of mucin. Other fibers are also observed, which are dis- 

 tinguished by a straight course, a sharp, well-defined outline, a tendency to 

 branch and unite with adjoining fibers, and to curl up at their extremities 

 when torn. From their color and elasticity they are known as yellow elastic 

 fibers. Distributed throughout the meshes of the areolar tissue are found 

 flattened, irregularly branched, or stellate corpuscles, connective-tissue 

 corpuscles, plasma cells, and granule cells. 



Adipose Tissue. This tissue, which exists very generally throughout 

 the body, though found most abundantly beneath the skin, around the 

 kidneys, and in the bones, is practically but a modification of areolar tissue. 

 In these situations it presents itself in small masses or lobules of varying 

 size and shape, surrounded and penetrated by the fibers of connective tissue. 

 Microscopic examination shows that these masses consist of small vesicles o 

 cells, round, oval, or polyhedral in shape, depending somewhat on pressure. 

 Each vesicle consists of a thin, colorless, protoplasmic membrane, thickened 

 at one point, in which a nucleus can usually be detected. This membrane 

 incloses a globule of fat, which during life is in the liquid state. It is com- 

 posed of olein, stearin, and palmitin. The origin of the fat is to be referred 

 to a retrograde change in the protoplasmic material of the connective-tissue 

 cells-. When this protoplasm becomes rich in carbon and hydrogen, it is 

 speedily converted into fat, which makes its appearance in the form of minute 

 drops in different portions of the cell. As the drops accumulate, at the ex- 

 pense of the cell protoplasm they gradually coalesce, until there remains 

 but a thin stratum of the protoplasm, which forms the wall of the vesicle. 

 Adipose tissue may, therefore, be regarded as areolar tissue, in which and at 

 the expense of some of its elements, fat is stored for the future needs of the 

 organism. A diminution of food, especially of fat and carbohydrates, is 

 promptly followed by an absorption of fat by the blood-vessels and by its 

 transference to the tissues, where it is either utilized for tissue construction 

 or for oxidation purposes. In the situations in which adipose tissue is found 

 it seems, by its chemic and physical properties, to assist in the prevention of a 

 too rapid radiation of heat from the body, to give form and roundness, and 

 to diminish angularities, etc. 



