Materials and Methods -- Observations -- Motoneuronal Centers and Neighbor Regions -- Sensory Relay Centers and Neighbor Regions -- Specific Precerebellar Centers -- Other Well Outlined Centers -- Diffuse Reticular and Tegmental Regions -- Midline and Paramedian Nuclei of the Brain Stem -- Subependymal Regions -- Discussion -- 1. Cholinergic Transmission in the Nervous System -- 2. The Significance of a Positive AThChE Stain -- 3. The Distribution of Acetylthiocholinesterase in the Brain Stem -- Summary -- Abbreviations -- References