HUMAN PHYSIOLOGY. 



ments of this form of connective tissue are united by a ground 

 substance, gelatinous in character. In the adult state this sub- 

 stance 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, transparent, wavy fibers, which are 

 cemented together by a ground substance composed largely of 

 mucin. Other fibers are also observed, which are distinguished 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, con- 

 nective-tissue corpuscles, plasma cells, and granule cells. 



Adipose Tissue. This tissue, which exists very generally through- 

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

 the kidneys, arnd 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 or cells, round, oval, or poly- 

 hedral in shape, depending somewhat on pressure. Each vesicle con- 

 sists 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 composed of olein, stearin, and palmitin. The origin of the 

 fat is to be referred to a retrograde change in the protoplasmic ma- 

 terial 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 expense 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 



