In a previous communication1we analyzed the pneumographic findings in cases of tumor of the brain involving the lobes of the cerebrum and outlined a form which we have used in their study. The present paper analyzes the findings in the remainder of the one hundred and twenty cases in which the diagnosis of tumor was verified. It includes the cases of tumor involving the basal ganglia, lateral ventricles, brain stem and cerebellum. TUMORS OF THE POSTERIOR FOSSA A tumor of the posterior fossa causes the greatest degree of hydrocephalus. It dilates all parts of the ventricular system above the block. This dilatation is seen to be symmetrical, when the ventricular system is satisfactorily drained. The lateral ventricles are round in all portions, and the third ventricle is greatly dilated. In this part of the system no constant factor has been found that is of value in determining the