[Crystallization and dissolution of collagen fibrils during the histogenesis of the intervertebral disk]

We studied the modifications of collagen fibrils during the histogenesis of the intervertebral disc of cats. In connexion with these studies it is necessary to distinguish between the fibrillar (functional) structure, the arrangement of fibrils, and the nature of fibrils, their diameter, period and other properties. Collagen fibrils (40--50 nm) of the anulus fibrosus enter in hyaline cartilage and split off in thin fibrils (8--10 nm). In this area the cartilage fibrils have a diameter of 20--22 nm, in a greater distance the diameter is diminished to 7--8 nm. Analogous to the changing of the nature of fibrils, the number of the cells related to the sectional area is diminished. The cells of the anulus fibrosus resemble those of tendons. In the transition area their shape becomes roundish, the number of granular membranes is increased, a voluminous Golgi-Apparatus appears for a short time. Finally, the cells are once transformed in cartilage cells with a small reticulum or cells of fibrocartilage with a capsule and a decreased cytoplasm; some cells are disintegrated. In the capsule of the fibrocartilage cells, parallel orientated filaments exhibit a periodical arrangement. In the border of the capsule, filaments change into periodical fibrils. Therefore, we must regard cells and their surrounding intercellular substance as metabolic unity which in the cartilage may be characterized as the chondron.