"afferent" impulses from without, are still fulfilled. The nerves which govern the muscles of the iris must be so affected by the imagination (or by some unknown agent acting only during sleep) as to contract, as if light still fell upon them. This does not seem, however, to concur with the generally accepted view that the muscular fibers that control the iris are involuntary. Until these extraordinary phenomena are understood, we shall doubtless not arrive at a complete theory of sleep. The study of dream phenomena will in this connection (in spite of Prof. Foster) constitute an essential aid.
The collateral phenomena accompanying and related to sleep, though not confined to natural sleep—or, for that matter, to any kind of sleep that suspends the bodily functions—are several. Dreams are the most important and significant; but we can give space only to some partial consideration of the two species of dreams namely, sleeping and waking dreams. Our encyclopædia of 1778 discusses several views then entertained regarding dreams; among them the curious one presented by the famous Richard Baxter, in his book on the Immateriality of the Human Soul, to the effect that dreams are due "to the action of some immaterial beings upon our souls." Objection is made to this on the ground that the existence of such immaterial beings is incapable of proof. This spiritualistic side of the discussion we must omit.
The most important suggestion regarding dreams made by this encyclopedist of 1778 is that mania and hypochondriasis are conditions under which the subjects dream while otherwise wide awake. That this is so appears incontrovertible, and we learn thence that the dream state does not necessarily arise from sleep, of the body at least. Mania may probably be defined as a dreamy slumber of the mind, without the participation of the body. Similar conditions are abundantly brought on temporarily by the abuse of certain powerful agents that destroy the rule of the will and reason over the mental functions, leaving the individual to be swayed altogether by the animal emotions. When the mania is chronic, accounts agree that in time the demoralization becomes, in most cases, so complete as to really give color to the views in ancient books, including our scriptural writings (and, moreover, in the works of some modern writers), that many if not most maniacs are under demoniacal possession. Waking dreams and reveries are known also to attack many persons in whose minds imagination is a predominating element. And even such as do not belong to this class, may become, when under the influence of great distress, fear, privation, or hardship, subject to such waking visions. Starvation or thirst, or both, have often produced the most remarkable illusions. One interesting example may be cited which is historical. It is found in the Journal of Strain's Ex-
