In civil life, bacterial invasion of the brain resulting in the formation of an abscess, occurs relatively infrequently. Such lesions usually follow as a slow extension from a septic process in the neighborhood of the brain and only reach it after erosion of bone and the heavy connective tissues of the meninges. The development may involve weeks or years. It is fortunate that the central nervous system is so well protected from invasion, as the septic injuries of the brain are the most distressing wounds that a surgeon has to handle. During active warfare, on the other hand, the number of such casualties is enormously increased, and this study was begun with the hope of improving the treatment of these cases. Unfortunately, such a program has been but partially carried out and the work here presented represents the histologic control of the experimental traumatic abscesses of the brain. The first