Histological Procedures

The fixed brain was embedded in ether-alcohol for a few hours and then a succession of ether-alcohol and celloidin mixtures of increasing viscosity, until the brain was suspended in a hard celloidin block.

Hundreds of thin sections (25-40 microns thick) were sectioned sequentially from this celloidin block. Each brain was sectioned serially using a standard sliding microtome. Most specimens were sectioned in a coronal plane. A few specimens were sectioned horizontally and a few were sectioned sagittally.

Alternate sections were then stained with thionin to stain nerve cell bodies, or hematoxylin to stain the myelin sheaths of nerve fibers (axons). The sections were stained according to an evolving recipe perfected over the years by the chief histologist, depending on the age and size of the specimen.

The cell-stained series were mounted on one set of slides and the fiber-stained series were mounted on another set of slides. All mounted sections were covered with thin cover slips and allowed to dry. They were then placed back to back in brain slide boxes, arranged from front to back (rostro-caudally, medio-laterally, or dorso-ventrally).

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