RHINORRHOEA 49 patient is recumbent the fluid passes into the nasopharynx. Cerebrospinal fluid contains a reducing substance, but this is not diagnostic as lacrimal secretion also reduces Fehling's solution. Radiography and tomography of the skull may locate the underlying lesion. The source of the fluid may be tested for by placing two pledgets of cotton-wool into the anaesthetized nose, one in the spheno-ethmoidal region in the olfactory cleft and the other in the posterior part of the middle meatus. At lumbar puncture 1 ml of 5 per cent fluorescein is injected and the patient is laid flat with his head dependent. Examination under ultraviolet light will detect the dye. If the cerebrospinal fluid arises from the frontal sinus the dye is anterior to the meatal wool; if from the cribriform plate the wool in the olfactory cleft is stained; and if from the sphenoidal sinus the dye will be found in the nasopharynx on posterior rhinoscopy. Spontaneous recession may occur, but the presence of a leak exposes the meninges to infection from the nose. Antibiotics may be used on a long-term basis to prevent this, and they are used should meningitis develop. Intranasal medication or surgery is contra-indicated in this condition. Surgical repair of the dural defect and the inlay of a strip of fascia lata to seal the cribriform plate, the inner table of the frontal sinus or the sphenoid sinus may be undertaken once the defect has been located.