At first sight there does not seem to be much chance that two such pathologically different conditions as intracranial tumor and Bright's disease could be confounded, and yet the error of mistaking one of these conditions for the other is not very uncommon. After all, the two conditions have many symptoms in common, especially if a brain tumor be in a so-called silent region. In both there may be headache, vomiting, eye changes, and even localizing symptoms, such as unilateral convulsions or hemiplegia. It is true that in certain forms of Bright's disease, those in which there is edema, anemia, and large amounts of albumin in the urine, mistakes are not likely to occur, but in the chronic interstitial form, in which edema may be slight or absent, and in which the urine may contain little and at times no albumin, the matter is not so simple. The differentiation is