Is the solitary dark neuron a manifestation of postmortem trauma to the brain inadequately fixed by perfusion?

Dark neurons, classified as solitary because of their sparse occurrence, were discerned in the transitional zones between gray and white matter in various species of laboratory animals fixed by perfusion. These neurons, histologically indistinguishable from dark neurons in immersion fixed material, tended to develop when the saline perfusion was delayed or slow, the amount of the Bouin fixative was excessive, or the autopsy was performed shortly after the perfusion. Under these conditions, the white matter manifested a softer consistency and a paler color than the gray matter. These observations suggest that, as the consequence of regional differences in intensity and speed of fixation, distortion during extraction of the brain may activate a stress force in the transitional zones where incompletely fixed neurons become affected and acquire an abnormal affinity for aniline dyes and silver.