I am aware however of the obscurity and difficulty of this subject itself, as well as the difficulty of expressing in accurate language, the ideas which arise in my own mind concerning it. I have used the term paralysis in speaking of the state of the diaphragm and other muscles during the paroxysm of Night-Mare; this expression however, must be understood in a different manner from that in which it is usually applied in medicine; for in Night-Mare there remains always a consciousness of the inability to move the muscles, and constant attempt at the same time to move them; this appears to be as constantly impeded by some external force acting against the efforts of the will: thus, when my hand and arm are lying uncovered, and in a position which easily admits of moving it, I am able, by repeated exertions, at length to raise it and bring it to my head, but the effort which it requires is equal to what in the waking state, would raise a covering, which might be laid over it, of twenty pounds weight: should a part of the sheet, or even a handkerchief be lying over the arm thus situated, the difficulty would be greatly increased; and the operation, if effected, would so much exhaust me, that I should be obliged to desist for some time from any further struggling, and the respiration at the same time would be greatly accelerated. Nothing of this kind occurs in paralysis, properly so called; for the patient is not even able to direct any effort of the will to the paralyzed muscles, and frequently is scarcely conscious of their existence. These two kinds of paralysis evidently differ considerably from one another, and ought not to be expressed by the same term.