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Examination of brain biopsies from Alzheimer's patients by electron microscopy revealed two types of filaments in and around the argyrophile plaques. The first neurofibrillary tangles were in degenerating neuronal processes, and each twisted tubule was made up of paired helical filaments. The second type stained for amyloid and had the ultrastructural appearance of amyloid. Amyloid fibril material found in these plaques was studied by means of tilt-stage electron microscopy and compared with X-ray images of scale models of bifilar helix. The model fulfilled the structural criteria established by electron microscopy. These observations confirmed that each amyloid profile was composed of a pair of twisted tubules, each of which measured about 60 A in diameter.
H.K. Narang (Sat,) studied this question.