It is difficult not to suppose something like this scattered condition of mind to be the usual state of brutes when not actively engaged in some pursuit. Fatigue, monotonous mechanical occupations that end by being automatically carried on, tend to produce it in men. It is not sleep; and yet when aroused from such a state, a person will hardly be able to say what he has been thinking about.

James, William. The Principles of Psychology. New York: Henry Holt, 1890. 404. Google Books. Web. 29 July 2010.