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Uncalibrated flow in the vertebral arteries was registered with a bidirectional CW Doppler ultrsound apparatus. It was applied to 20 patients, results being compared with aortic arch angiograms in which the extracranial part of all four cerebral vessels was seen. In 14 the vertebral arteries had a symmetrical flow and lumen, a similar symmetrical result being obtained with the Doppler. Hypoplasia of one vertebral artery was present in two patients the distinct asymmetry being recorded by the ultrasound. Three patients with central stenosis in one subclavian artery and subclavian "steal" were found to have reverse flow by the Doppler method in the vertebral artery on the side of the stenosis. Endarterectomy was performed on the affected subclavian artery in two of these patients: post-operative vertebral ultrasound recordings demonstrated a return to physiological flow direction in both vertebral arteries.

White-cell count and differential blood count, total protein, lactate dehydrogenase activity (E.C. 1.1.1.27) and lactate concentration were determined in 496 CSF samples, obtained by lumbar puncture. Lactate was measured with a new enzymatic test. Reference values were determined for lactate and lactate dehydrogenase (90% limits: 1.2-2.1 mmol/l and 6-26 U/l, respectively). Lactate content proved to be best in the differential diagnosis between acute bacterial and abacterial meningitis: concentrations of 3.5 mmol/ml and above were found exclusively in bacterial meningitis. As for other diseases, markedly increased lactate concentrations were measured only in patients with brain tumour or cerebrovascular disease (up to 9.3 mmol/l). Determination of lactate concentration alone would have led to a misdiagnosis of acute bacterial meningitis in 3% of cases. If the CSF contains 3.5 mmol/l lactate or more and the leucocyte cell count is above 800/microliter, brain tumour or cerebrovascular disease can be practically excluded and the diagnosis of bacterial meningitis made with a high degree of reliability.