In M. Maury’s own case he finds that the hallucinations are more numerous and more vivid when he experiences, as is frequent with him, a disposition to cerebral congestion. Thus, when he has headache, nervous pains in the eyes, the ears, and the nose, and vertigo, the hallucinations make their appearance as soon as he closes his eyelids. Loss of sleep and severe intellectual exertions invariably produce them, as do also _cafe noir_ and champagne, which, by causing headache and insomnia, strongly predispose him to the hypnagogic hallucinations. On the contrary, calmness of mind, rest, and country air lessen his liability to them. From the inquiries made of others by M. Maury, the results of his own experience, as well as from my own observations, I am well convinced that the hypnagogic hallucinations are directly the result of an increase in the amount of blood circulating through the brain rather than to actual congestion as he supposes. They therefore indicate the existence of a condition unfavorable to sound sleep. In the chapter devoted to the consideration of wakefulness the phenomena accompanying cerebral hyperæmia will be more fully considered. The theory which M. Maury proposes in order to account for the existence of hypnagogic hallucinations further presupposes that as the power of the attention immediately before sleep begins to be diminished, and the mind cannot therefore voluntarily and logically arrange its thoughts, it abandons itself to the imagination, and that thus fancies arise and disappear unchecked by the other mental faculties. This absence of the attention need not be of long duration, a second, or even a shorter period being sufficient. Thus he lay down, and the attention which had been fully aroused soon became weakened; images appeared, and these partially reawakened the attention, and the current of his thoughts was resumed, to be replaced again by hallucinations, and this continued till he was fully asleep. As an example, he states that on the 30th of November, 1847, he was reading aloud the _Voyage dans la Russie Méridionale_, by M. Hommaire de Hell. He had just finished a line when he closed his eyes instinctively. In this short instant of sleep he saw hypnagogically, but with the rapidity of light, the figure of a man clothed in a brown robe, and with a hood on his head like a monk. The appearance of this image reminded him that he had shut his eyes and ceased reading. He immediately opened his eyelids and resumed his book. The interruption was practically nothing, for the person to whom he was reading did not perceive it. M. Maury gives numerous examples of these hypnagogic hallucinations, all tending to show that they are induced by a congested condition of the cerebral vessels, and that thus, according to the views I have set forth relative to the condition of the brain in sleep, they are not to be regarded as precursors of that state, but of stupor.