The _diffuse septic meningitis_ is the most discouraging intracranial complication that we have to deal with, and the diagnosis as a rule is not difficult. It usually is preceded by the serous form, but within a very short time develops the graver symptoms of sepsis. The most positive symptom is the spinal puncture. The fluid comes out under pressure, but not so great as in the serous form, and is turbid. The turbidity varies in degree with the amount of infection. It has the appearance at times of pure pus; in fact, that is what it is. Bacteriologically one will find many micro-organisms of the character of the infection; and leucocytes or pus cells are very numerous. The sugar reaction is always absent, and the acidity is much increased as is the quantity of cholin. The pressure or irritative symptoms as the Kernig and Babinski tests, as well as the pupillary reactions, are practically the same as in the serous meningitis, only that they soon give away to the paralytic form, namely: pupils dilate, patient is in a constant stupor or coma, and the involuntary urination and bowel movements become very manifest. The patient is, as a rule, unable to take or be given nourishment. The outcome is, in my experience, with one exception, always fatal, due to diffuse cerebritis. I have had a case of diffuse septic meningitis in the early stages of a pneumococcic type which I operated on by the Haynes’ method of drainage of the cyscterna magna, and which recovered; and I believe that the success in that case was due to the very early intervention, because I have operated by the same method on eight other cases more advanced and of streptococcic and staphylococcic type of infection, which ended fatally.