The mental processes in relation to vision are disordered in many cases of mental disease, particularly in such as present the symptom of disorientation. The normal individual orientates himself in his environment mainly by the help of definite trains of visual ideas—such, for example, as are aroused in us when we glance round our room, go about the house, or take a walk out of doors. If a patient in an asylum thinks he is in his own home, and mistakes the attendants for his relatives, he is clearly unable to see how the present environment differs in aspect from the former environment in which he imagines himself. While from one point of view such a disability presents itself as a failure of memory, from another it appears as a form of mind-blindness, demonstrable by appropriate tests, and resembling in some ways the mind-blindness resulting from circumscribed coarse damage of the brain.