THE CONNECTIVE TISSUES. 



33 



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. (See Fig. 6.) Microscopic examination shows that these masses 

 consist of small vesicles or cells, round, elliptical or polyhedral in shape, 

 depending somewhat on pressure. (See Fig. 7.) 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 composed 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 proto- 

 plasm becomes rich in carbon and hydrogen, it is speedily converted into 

 fat, which makes its appearance in the form of minute drops in different 



In 



super- 

 posed 

 layers. 



FIG. 6. ADIPOSE TISSUE. (Stokr.) 



FIG. 7. FAT-CELLS FROM THE 

 AXILLA OF MAN. i. The equator 

 of the cell in focus. 2. The ob- 

 jective somewhat elevated. 3, 4. 

 Forms changed by pressure, p. 

 Traces of protoplasm in the vicinity 

 of the flat nucleus k.(Stohr.) 



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 either utilized for tissue construction or for oxida- 

 tion purposes. In the situations in which adipose tissue is found it serves, 

 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. 



Retiform and adenoid tissue are also modifications of areolar tissue. 

 The meshes of the former contain but little ground substance, its place being 

 taken by fluids; the meshes of the latter contain large numbers of lymph 

 corpuscles. 



Fibrous Tissue. This variety of connective tissue is widely distributed 



throughout the body. It constitutes almost entirely the ligaments around 



the joints, the tendons of the muscles, the membranes covering organs such 



as the heart, liver, nerve system, bones, etc. All fibrous tissue, wherever 



3 



