Having met from time to time with cases of brain-fag, and also actual insanity, arising from excessive mental work, I wish to direct attention to-day to this cause of disordered mind, not because it is so wide-spread a cause as many others, but because for this very reason it is in danger of being treated with indifference, whereas at the present moment I regard it as a serious evil, although comparatively restricted in its operation in consequence of the great mass of the people falling under opposite influences; still I fear that it is in schools and colleges as well as in the cottage of the labourer and manufacturer, among students as well as among those who delve and spin, that we must seek for the causes of mental disturbance if we wish to understand them thoroughly.