THERE are few problems in neuropathology of wider practical significance than that of the fundamental understanding of the nature and extent of cerebral lesions arising from head trauma. Both neurosurgeon and neurologist are frequently confronted with the question: What are the pathologic and physiologic changes in the brain of a patient who, after cerebral injury, complains of a great variety of neurologic or mental disturbances? Evaluation of the degree of damage to the brain occurring in countless cases of post-traumatic invalidism is of the greatest importance, not only for the practicing physician but also for the judge and lawyer. Correct evaluation of the actual role played by trauma in such cases involves a number of questions which are not to be answered without a more profound knowledge of the widespread pathologic alterations that follow injury to the central nervous system. In years past, a detailed study of skull fracture, meningeal