Another large class of psychological phenomena, which has been productive of more conflicting theories than any other, and which from time immemorial has puzzled and appalled mankind, is by a large class of persons referred to the direct agency of the spirits of the dead. It would require a volume to catalogue the various theories which have been advanced to account for this class of phenomena, and when done it would serve no useful purpose. It is safe to say, however, that no two individuals, whether believers or unbelievers in the generic doctrine of spiritism, exactly agree as to the ultimate cause of the phenomena. The obvious reason is that no two persons have had exactly the same experience, or have observed exactly the same phenomena. In the absence of a working hypothesis applicable to all the infinite variety of facts observed, it follows that each investigator must draw his own conclusions from the limited field of his own experience. And when we take into consideration the important _rôle_ which passion and prejudice ever play in the minds of men when the solution of an undemonstrable problem is attempted, it is easy to see that a bewildering hodge-podge of heterogeneous opinions is inevitable. Another class of phenomena, about which an infinite variety of opinions prevails, may be mentioned under the general head of mental therapeutics. Under this generic title may be grouped the invocations of the gods by the Egyptian priests; the magic formulas of the disciples of Esculapius; the sympathetic powder of Paracelsus; the king's touch for the cure of goitre; the wonderful cures at the tomb of Deacon Paris and at Lourdes; the miraculous power supposed to reside in the relics of the saints; the equally miraculous cures of such men as Greatrakes, of Gassner, and of the Abbot Prince of Hohenlohe; and the no less wonderful healing power displayed by the modern systems known as mind cure, faith cure, Christian science, animal magnetism, and suggestive therapeutics.