IN order to understand venous stasis in its several relationships to the functions of the brain, it is advisable to refer to some of the problems which have been the most difficult with which neurologists and psychiatrists have had to deal. The aspects of the problems studied have been so varied, and the interpretations of the phenomena so widely different, that it has hitherto been almost impossible to obtain any degree of unanimity of opinion. In dealing with the aetiology and pathology of disease one of the first considerations ought to be to determine, if possible, the existence of physical or mechanical factors of causation.