54 



THE CONNECTIVE TISSUES 



the fibrils become swollen. They are digested by acid solutions of 

 pepsin. In preparing slides to show them, fixing solutions contain- 

 ing acetic acid should be avoided since it causes swelling and 

 distortion of the collagenous material. They are stained by eosin 

 and other acid dyes but stand out sharply with aniline blue. Their 

 jiroperties appear to show some variation in dift'erent regions of the 

 same animal as well as in difi^erent animals. They do not stretch, 

 but through their arrangement in networks adapt themselves to 

 possible expansions of the tissue by changes in the meshes. 



Elastic i^iter^.— Homogeneous threads or small bands of varying 

 size occur as distinct, refractive, and non-fibrillar elements. They 



are composed of a compound 

 called elastin, and branch to 

 form a network. These fibers 

 are decidedly elastic; under 

 tension they stretch but resume 

 their original form when re- 

 leased. When they are broken 

 the ends curl up. Grouped in 

 large numbers, these fibers ap- 

 pear yellow in color. They are 

 not affected by boiling in weak 

 acids, or alkalies, but are slowly 

 digested in solutions of pepsin 

 and trjqjsin. Specific stains, 

 such as resorcin-fuchsin and 

 orcein make them stand out as 

 distinct branching threads in 

 preparations. Through combination with one another these fibers 

 form bands or membranes in the walls of large arteries. 



Function.— Loose fibroelastic connecti^•e tissue forms a strong 

 elastic material which is light and flexible and adapted to holding 

 together other tissues which are especially concerned with secretion, 

 absorption, movement, storage, and conduction. It is the chief 

 tissue for the support of the blood vessels and the capillary networks 

 supplying nutrition and oxygen to the tissues involved in secretion 

 and excretion. Furthermore, before reaching other cells both food 

 and oxygen must pass from the cai)illaries into the groimd substance 

 or tissue juice of this tissue. Likewise, such wastes of metabolism 

 as urea, carbon dioxide, and water pass through the tissue juice on 

 their way to the capillaries prior to elimination. Thus, the element 



Fig. 31. — Diagram of loose fibroelastic 

 connective tissue. 1, bundles of collagen- 

 ous fibers; 2, elastic fibers. Tissue spaces 

 are indicated between the fibers. 



