Recently the lateral width of the cellulose microfibril has been estimated as 30 A rather than about 150 to 200 A, by extrapolation of data from model shadowing experiments. The difference was attributed to a layer of metal deposited during shadowing. However, direct photographs of the same microfibrils parallel and perpendicular to the direction of shadowing, of unshadowed portions of microfibrils compared with shadowed portions of the same microfibrils, of silver-stained unshadowed microfibrils, and of unshadowed, unstained segments of microfibrils give no evidence of a layer of metal of this thickness in material shadowed under normal conditions. Furthermore, the evidence for microfibril strands of about 35 A in width from negative-staining experiments is subject to a bias from the form of the filaments and from variable positive adsorption of phosphotungstic acid by cellulose. Consequently, the conclusion that the true lateral width of native cellulose microfibrils is about one-fifth of the presently accepted value is not yet justified by unequivocal direct experimental evidence.

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