It is difficult to say whether Mohammed, who had undoubtedly visions innumerable, received any aid from his hallucinations in devising his new faith. Men of science tell us that he suffered of _Hysteria muscularis_, a disease not uncommon in men as well as in women, which produces periodical paroxysms and is characterized by an alternate contraction and expansion of the muscles. When the attack came the prophet's lips and tongue would begin to vibrate, his eyes turned up, and the head moved automatically. If the paroxysms were very violent he fell to the ground, his face turned purple, and he breathed with difficulty. As he frequently retained his consciousness he pretended that these symptoms were caused by angels' visits, and each attack was followed by a new revelation. The disease was the result of his early lawless life and of the freedom which he claimed, even in later years--pleading a special dispensation from on high as a divinely inspired prophet. It is not to be wondered at that the new religion, springing from such a source, and proclaimed amid the mountains and steppes of Arabia, which, according to popular belief, are all alive with djinns and demons, should be largely based upon visions and hallucinations. The important part which visions hold in the history of the various religions of the earth lies beyond our present purpose; we know, however, that the records of ancient temples, of prophets, saints, and martyrs, and of later convents and churches, abound with instances of such so-called revelations from on high. They have more than once served at critical times to excite individuals and whole nations to make sublime efforts. One of the best known cases of the former class is that of Constantine the Great, who told Eusebius of Cæsarea, affirming his statement with a solemn oath, that he saw in 312, shortly before the decisive battle at Rome against his formidable adversary Magentius, a bright cross in the heavens, surrounded by the words: _In hoc signo vinces_. But this vision stood by no means alone. He himself beheld, besides, in a dream during the following night, the Saviour, who ordered him to use in battle henceforth a banner like that which he had seen in his vision. Nazarius, a pagan, also speaks of a number of marvelous signs in the heavens seen in Gaul immediately before the emperor's great victory. Nor can it be doubted that this vision not only inspired Constantine with new hopes and new courage, enabling him to secure his triumph, but also induced him, after his success, to avow himself openly a convert to the faith of Christ.