Of all the physical phenomena which interest philosophers and psychiatrists there are none more interesting than hallucinations. Psycho-sensory disorder is a complex aggregate in which the psyche in its entirety is mingled with organic disorders, an association which is still a mystery to us. The study of the affective states in the hallucinated is, therefore, of the highest importance, since it allows us to bring psychic and physiological disorders together in their reciprocal relations. “The hallucination,” says Hesnard, “which has always for the patient a personal affective significance more or less distinct, is only the symbolical translation, in comparison with a normal perception, of an interior positive psychic fact, of an affective productivity.”