Meningitis is presumed to arise in one of three general ways: Organisms may reach the subarachnoid space by direct traumatic implantation; infection may extend to the meninges from an adjacent lesion, as in some cases of virulent mastoiditis with progression of the infection through the temporal bones, or organisms gaining access to the general circulation from a focus of infection at any site, however remote, may succeed in reaching the meninges by passing the blood-brain barrier.
Lumbar puncture, performed for diagnosis, entails the risk of producing meningitis. The danger involved in a break in aseptic technic is clearly visualized and constantly borne in mind. Other dangers, related to the effect of lumbar puncture on the permeability of the blood-brain barrier and to the possibility of introducing bacteria-containing blood into the subarachnoid space, are less clearly understood and at times seem to be ignored. The uncertainty which surrounds the latter factors