The work discussed in this paper was undertaken with the view of determining, first, whether there are any chemical and physicochemical changes in the cerebrospinal fluid of meningism in addition to the physical changes very apparent in every case; and second, whether the chemical and physicochemical changes noted in the cerebrospinal fluid of meningitis, differ chemically and physicochemically only quantitatively or qualitatively as well in the various forms of the disease. In this study particular attention was paid to the question of acidosis—to which a great deal of prominence was given by Kopetzky,1 who holds that "the predominance of the pressure symptoms as found in meningitis is in large measure due to a state of edema of the cerebral and meningeal tissues, and the edema is, in turn, the result of an acidosis evidenced clinically by the varying degree of acidity found in the cerebrospinal fluid." According to