How it is that man sleeps is a question which has caused an extraordinary amount of perplexity to philosophers. But yet our prophet has distinctly explained this question; for sleep is in itself properly a trance, not of that kind which is more nearly allied to insanity, but of that which is in accordance with the dissolution of the senses and the absence of counsel; for then the senses withdraw from those things which are their proper object, and the intellect withdraws from the senses, not strengthening their nerves, nor giving any motion to those parts which have received the power of action, inasmuch as they are withdrawn from the objects perceptible by the outward senses.