With the introduction of lumbar puncture the diagnosis of acute meningitis entered on a new phase. This is quite as important an advance in this group of diseases as was the adoption of throat cultures in diphtheria and other throat affections. Exact diagnosis has now become possible where formerly in very many cases only a probable diagnosis could be made. The period during which lumbar puncture has been systematically performed on all suspected cases in the Babies' Hospital covers the last five years.
The observations included in this paper relate to 300 cases of acute meningitis seen in this hospital, in children for the most part under three years of age. Of this number 197 have been observed during the lumbar puncture period and are available for more careful analysis. Some valuable data obtained from the records of 103 earlier cases are introduced. In order to gain some idea of