While there are no known changes in the brain tissues in these diseases, it seems not improbable that the development of our knowledge of brain anatomy, which is especially active at the present time, will very soon demonstrate the minute lesions that are the basis of these mental disturbances. It seems not unlikely that the underlying cause of so-called idiopathic insanity is usually some change within the brain cells. Hints of the truth of this conjecture are already at hand. Meantime the actual observation of this class of patients in asylums and institutions, private and public, and the collation of the observations of authorities in psychiatry from all over the world, have thrown a great deal of light on these forms of mental disease. We know much more of the initial symptoms and of incipient conditions that threaten the development of mental {213} disequilibration than we did twenty-five years ago. With regard to prognosis especially, recent publications have added considerably to our knowledge, although it must be confessed that they have rendered our judgment of such cases much less hopeful. The ordinary forms of mental diseases have sometimes been considered as passing incidents in the lives of patients suffering from such disorders. While it was generally understood that severe cases were apt to have recurrences, and that after persistence of mental symptoms for a certain length of time the outlook as regards eventual absolute cure is rather dubious, yet the general prognosis of such simple states as melancholia or simple mania was not considered to be distinctly unfavourable. Patients might very well recover their mental sensibility after even a severe attack, and never have a relapse. It was something of an unpleasant surprise to the medical world, a few years ago, when one of the most distinguished authorities in Europe on the subject of mental diseases, Professor Kraepelin, of the University of Heidelberg, stated in his text-book of psychiatry, that among a thousand cases of acute mania he has observed only one in which the symptoms did not recur. Professor Berkley, of Johns Hopkins University, Baltimore, a conservative American authority, in discussing this subject of relapses after single occurrences of mania, is evidently of the opinion that Professor Kraepelin's opinion in the matter presents the inevitable conclusion that must be drawn from recent advances in the clinical knowledge of maniacal conditions. "Simple mania," he says, "is, according to the statistics now at hand, an exceedingly rare form of mental disease, and the physician should therefore be cautious in making a prognosis of final recovery. Relapses after a number of years, when stability is apparently assured, are frequent, as every one interested in mental medicine knows only too well."