The object of this communication is to report the results obtained in a study of experimental acidosis in animals. The chief interest lies in investigation of the relationship between acid-base equilibrium in the blood and a similar equilibrium in the cerebrospinal fluid. The study of such a relationship, namely, of certain conditions under which artificial acidosis in the blood reflects on the acid-base balance in the cerebrospinal fluid, was inspired by bibliographic data of twofold nature: (a) publications of the last few years attributing great significance to acidosis in mental disorders1and to acidosic treatment (with a ketogenic diet) in epilepsy,2and (b) reports contending that blood substances reach and affect the nerve tissues mainly through the intermediation of the cerebrospinal fluid.3 TOPICS AND METHOD OF STUDY In the light of the observations that the acid-base equilibrium of the cerebrospinal fluid is markedly more stable than the