234 MACROMOLECULAR COMPLEXES 



The fibers consist of a core of protein, sometimes completely in- 

 cased in polysaccharide. When the coating is not complete (Fig. 3), 

 however, it can be seen to consist of fibrils running spirally round 

 the fiber. The inclination of the fibrils to fiber length varies broadly 

 around 72° (cf., the value of 75° in elongated, growing plant cells- 

 Preston, 1947; Preston and Wardrop, 1949; Middlebrook and Pres- 

 ton, 1952). 



Fig. 3. Antisotropic fiber from bovine epidermis with incomplete polysaccha- 

 ride sheath, as seen between crossed nicols. The polysaccharide appears 

 bright, the protein core dark. X520. 



The composition of the protein core difiers from that in collagen 

 and elastin. Like elastin, the protein is rich in glycine, proline, and 

 valine; it contains some hydroxyproline but less than does collagen. 

 On the other hand, appreciable quantities of acidic and basic amino 

 acids are present, a feature more characteristic of collagen. 



It is not, of course, certain that the cellulose is svnthesized in situ; 

 the conclusion does, however, seem inescapable that the protein, a 

 degenerative product of collagen, is involved in at least the orienta- 

 tion of the cellulose. 



