CONNECTIVE TISSUE 



cells may migrate. There are no capillaries, lymphatic vessels, or nerves 

 within the mucous tissue of the umbilical cord, and no elastic fibers. The 

 three large blood vessels which pass through the cord, and the tissue in 

 their walls, will be considered later. 



CONNECTIVE TISSUE. 



Connective tissue occurs in various forms. Dense connective tissue 

 is a tough fibrous substance, such as that part of the skin from which leather 

 is made; and loose connective tissue, or areolar tissue, is a spongy cobweb 

 of delicate filaments, such as occurs between the muscles. Both forms 

 when fresh are very white, and they are composed of similar fibers, A 

 small mass of fresh connective tissue, subcutaneous or inter-muscular, 

 may be spread out with needles upon a slide, thus forming a thin film. 

 After adding a drop of water and applying a cover glass, it will present 



FIG. 53. SUBCUTANEOUS TISSUE FROM A CAT. 



The fiber a has been treated with dilute acetic acid; the other fibers have been teased apart and examined, 

 unstained, in water, a, c, White fibers; b, fat cell; d, connective tissue cell; e, elastic fibers. 



such an appearance as shown in Fig. 52. The bulk of the tissue is seen 

 to consist of white or collagenous fibers felted together (Fig. 52, c). They 

 are the same in origin and structure as those already described in the 

 mucous tissue of the umbilical cord, but in ordinary connective tissue 

 their fibrils are gathered into denser bundles. Each bundle or fiber is 

 composed of exceedingly minute fibrils, bound together by a small amount 

 of cement substance. The addition of picric acid causes the fibers to 

 separate into their constituent elements. Often a bundle of fibrils turns 

 aside from the main trunk, so that the fiber branches, but the fibrils 

 themselves are unbranched. 



Upon the addition of dilute acetic acid the white fibers swell and dis- 

 integrate, some of them passing through the condition shown in Fig. 52, a. 

 Such fibers show a succession of constrictions at places where they are 

 encircled by rings or spiral bands of a refractive substance not affected 



5 



