Ultrastructure of native collagen.

: Native collagen fibrils, mechanically detached either from leg tendon of rabbits or from tail tendon or aortic adventitia of adult rats were observed at the electron microscope by various technical methods. The density patterns recorded along and across integer fibrils, laid down on ultrathin C films, show that the density ratio of the light to the dense bands is much higher than that expected from the generally accepted quarter-stagger arrangement of collagen unities. Swollen fibrils show long filaments, about 50 A thick, reasonably identified with their building unities. The characteristic collagen banding of about 640 A periodicity, never exhibited by single filaments, is already present in groups of very few filaments (order of two or three). Partially disrupted fibrils suggest that the building filaments may be assembled in a monolayer, having the form of a long ribbon, spirally wound around the longitudinal axis of the integer fibril.