Immunologic study of the brain as a privileged site.

A number of experimental findings reported here indicate that the brain functions as a privileged site not because of an afferent arc blockade, as hitherto thought, but because of an efferent arc blockade, with some afferent arc delay. There appears to be a quantitative deficiency in the efferent arc, but a qualitative defect is not ruled out. Implants survive four times as long in the brain as in the anterior chamber.