But, notwithstanding Marracci’s eloquent plea for a more thorough study of Islam, his words fell, for the most part, on deaf ears.[237] It was not until our own epoch that a critical investigation of the Koran was begun and that a really impartial inquiry into the life of Mohammed was seriously undertaken. Men were still in doubt as to the true character of the Arabian reformer and were still undecided as to whether he was _Hero, impostor, fanatic, priest or sage._ All, however, were forced to admit that he must have been a man of extraordinary power and influence to set in motion that mighty human current which only a little more than a century after his death had founded an empire which extended from the Tigris to the Gaudilquivir and from the burning sands of Yemen to the chilly steppes of Turkestan. Yet, although the scholarly works of Sprenger, Margoliouth, Prince Caetani, and Noldeke-Schwally have thrown a flood of light on many formerly obscure points in the life of the Prophet and elucidated many previously disputed passages of the Koran, there is still as much discussion as ever regarding the nature of Mohammed’s religious vocation. Some contend that it was the result of hallucination, others of epilepsy, others of psychopathic abnormality, others of auto-hypnosis, while, as a result of long researches, Aloys Sprenger is quite sure that the Prophet was a victim of muscular hysteria.[238] But however much controversy there may be respecting the origin of Mohammed’s self-styled mission or the nature of the mental disease from which he is said to have suffered, there can be no doubt whatever about the essence of his teaching as incorporated in the Koran. For the creed of Islam is so simple that, as has been said, “it can be written on a fingernail.” The five duties of Islam, which means resignation to the will of God, as declared by Mohammed, are as follows: 1. Bearing witness that there is but one God; 2. Reciting the daily prayers; 3. Giving the legal alms; 4. Observing the Ramazan or the month’s fast; 5. Making the pilgrimage to Mecca once in a lifetime.