=Acute traumatic abscess.= Acute traumatic abscess of the brain most commonly arises in connexion with an infected compound fracture of the skull. In the event of laceration of the dura mater, infective organisms have a ready means of access both to the meninges and to the brain itself, meningitis or cerebritis resulting. This liability to meningeal and brain infection is increased when hair, portions of clothing, bullets, or other foreign bodies are embedded amongst the comminuted fragments of bone, or driven into the brain substance. In the event of the dura mater remaining intact, meningitis or cerebritis may still develop if, as the result of scalp suppuration, the diploic vessels become thrombosed and plugged with bacteria, some of which may be carried inwards by the reversed blood-stream, and perhaps by lymphatic connexions. The infection may remain localized to the adjacent brain substance, an acute traumatic cerebral abscess resulting, or may become more widely diffused--diffuse cerebritis--a condition usually associated with general meningeal infection. An acute traumatic cerebral abscess is almost necessarily situated immediately beneath the site of osseous and membranous lesion, being, in fact, more a meningo-cortical abscess than a brain abscess proper. The boundaries are but ill-defined, the walls ragged, and the contents of a brown-red colour. The surrounding brain is in a condition of red softening, that is to say, extensively infiltrated with leucocytes, the vessels thrombosed and teeming with bacteria, whilst minute extravasations of blood lead to the characteristic colour both of the contents of the abscess and of the surrounding tissue. In the more chronic cases, the surrounding area shows some attempt at repair, dense armies of leucocytes barring the way to the spread of the infection, and, in the more favourable cases, allowing of the formation of a definite fibrous barrier. =Symptomatology.= The symptoms resulting from an acute traumatic cerebral abscess are largely dependent on the site of the abscess. In the earlier stages of development suspicion may be aroused by the presence of persistent headache--frequently localized to the region primarily affected--by mental and bodily irritability, restlessness, and pyrexia. All these symptoms may, however, be produced by the unhealthy condition of the scalp-wound--free suppuration, bare bone, and extra-dural suppuration. On or about the third day, the condition of the patient becomes more grave, the change for the worse being usually of rapid development, and preceded by severe rigors and general convulsions. The patient shows further signs of mental irritation, being delirious, restless, and occasionally actually maniacal.