The Occurrence of Crystals within Collagen Fibrils

Earl ier electron microscope studies have provided circumstant ial evidence for the existence of crystals within the collagen fibrils 1 of bone matr ix. In fully calcified bone matr ix there are no areas which are not replete with crystals; a finding which indicates tha t there should be a deposition of crystals not only a t the per iphery of fibrils but within them as well (12). The posit ion of crystals along collagen fibrils has been shown by Jackson in sections from incompletely calcified embryonic avian bone (4, 5). She suggests, when referring to longitudinal ly oriented collagen fibrils with a t tached crystals, tha t the section plane may pass through the fibrils. This implies tha t crystals could lie within the fibrils. The present communicat ion reports the occasional finding of small crystals located within collagen fibrils during an early phase of calcification.