Neural tissues were impregnated en bloc with silver by a modification of Hortega's method customarily used to stain astrocytes in thin tissue sections for light microscopy. The tissue blocks were then embedded in methacrylate and sectioned at 1 micron and 25 millimicrons for light and electron microscopy. The former regularly showed the silver deposited selectively and in great quantities within the perikaryon and fine neuroglial processes of astrocytes. In electron micrographs, the argentophilic neuroglia had moderately abundant osmiophilic cytoplasm from which numerous argentophilic processes arose, forming a dense reticulum, but rarely ending perithelially. When considered together with observations upon neural tissues prepared by conventional methods for electron microscopy, the findings provide cogent evidence that astrocytes possess much osmiophilic, rather than water-clear periknryon and, although attached by foot-processes to blood vessels, do not ensheath the cerebral vasculature.
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