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.

Electron microscope identification of mesosomes in some water strains of Leptospira by reduction of tetrazolium chloride to formazans.

Rounded granules protruding from the external surface of some water Leptospira strains and considered as mesosomes were studied by electron microscope and by means of the intravital reduction of tetrazolium chloride. Satisfactory results were obtained with two of the strains studied. It appears that neither the culture medium nor the age of the culture have any influence on the unusual position of the mesosomes.

Ultrathin supporting films in electron microscopy of unstained biological macromolecules.

A simple technique is described, in which the increase in thickness of a carbon film is controlled. Films up to 10-15 A in thickness, which are both continuous and strong enough for use as supporting films in electron microscopy, can be easily obtained by this routine method. Images are shown of unstained ribosomial subunits and tropocollagen molecules on 15 A carbon films.